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 $178.53   13.714%   $203.0136   $203.01   $203.00   $203.00  
  Purchase #2 $131.89   13.759%   $150.0367   $150.04   $150.05   $150.00  
  Purchase #3 $232.93   12.805%   $262.7567   $262.76   $262.75   $262.80  
  Purchase #4 $213.52   9.643%   $234.1097   $234.11   $234.10   $234.10  
  Purchase #5 $61.91   6.546%   $65.9626   $65.96   $65.95   $66.00  
  Purchase #6 $5.59   9.312%   $6.1105   $6.11   $6.10   $6.10  
  Purchase #7 $58.49   4.331%   $61.0232   $61.02   $61.00   $61.00  
  7 purchase totals = $882.86       $983.0130   $983.01   $982.95   $983.00