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 $86.56   6.304%   $92.0167   $92.02   $92.00   $92.00  
  Purchase #2 $245.44   5.457%   $258.8337   $258.83   $258.85   $258.80  
  Purchase #3 $24.43   12.598%   $27.5077   $27.51   $27.50   $27.50  
  Purchase #4 $123.75   13.787%   $140.8114   $140.81   $140.80   $140.80  
  Purchase #5 $161.82   7.324%   $173.6717   $173.67   $173.65   $173.70  
  Purchase #6 $130.54   6.370%   $138.8554   $138.86   $138.85   $138.90  
  Purchase #7 $167.27   13.304%   $189.5236   $189.52   $189.50   $189.50  
  7 purchase totals = $939.81       $1,021.2202   $1,021.22   $1,021.15   $1,021.20