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 $201.50   7.456%   $216.5238   $216.52   $216.50   $216.50  
  Purchase #2 $122.95   7.659%   $132.3667   $132.37   $132.35   $132.40  
  Purchase #3 $150.54   9.382%   $164.6637   $164.66   $164.65   $164.70  
  Purchase #4 $200.83   5.305%   $211.484   $211.48   $211.50   $211.50  
  Purchase #5 $141.36   6.505%   $150.5555   $150.56   $150.55   $150.60  
  Purchase #6 $137.62   9.591%   $150.8191   $150.82   $150.80   $150.80  
  Purchase #7 $179.60   12.657%   $202.332   $202.33   $202.35   $202.30  
  7 purchase totals = $1,134.40       $1,228.7448   $1,228.74   $1,228.70   $1,228.80