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 $77.96   6.412%   $82.9588   $82.96   $82.95   $83.00  
  Purchase #2 $183.81   4.341%   $191.7892   $191.79   $191.80   $191.80  
  Purchase #3 $249.82   8.179%   $270.2528   $270.25   $270.25   $270.30  
  Purchase #4 $225.54   10.409%   $249.0165   $249.02   $249.00   $249.00  
  Purchase #5 $120.35   5.282%   $126.7069   $126.71   $126.70   $126.70  
  Purchase #6 $97.62   13.678%   $110.9725   $110.97   $110.95   $111.00  
  Purchase #7 $162.48   4.226%   $169.3464   $169.35   $169.35   $169.30  
  7 purchase totals = $1,117.58       $1,201.0431   $1,201.05   $1,201.00   $1,201.10