Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $194.36   6.754%   $207.4871   $207.49   $207.50   $207.50  
  Purchase #2 $182.73   10.274%   $201.5037   $201.50   $201.50   $201.50  
  Purchase #3 $121.52   8.537%   $131.8942   $131.89   $131.90   $131.90  
  Purchase #4 $150.64   8.640%   $163.6553   $163.66   $163.65   $163.70  
  Purchase #5 $206.35   7.529%   $221.8861   $221.89   $221.90   $221.90  
  Purchase #6 $229.88   11.198%   $255.622   $255.62   $255.60   $255.60  
  Purchase #7 $144.38   5.508%   $152.3325   $152.33   $152.35   $152.30  
  7 purchase totals = $1,229.86       $1,334.3809   $1,334.38   $1,334.40   $1,334.40