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 $61.63   5.796%   $65.2021   $65.20   $65.20   $65.20  
  Purchase #2 $43.92   7.319%   $47.1345   $47.13   $47.15   $47.10  
  Purchase #3 $8.92   9.309%   $9.7504   $9.75   $9.75   $9.80  
  Purchase #4 $97.51   9.511%   $106.7842   $106.78   $106.80   $106.80  
  Purchase #5 $27.96   11.303%   $31.1203   $31.12   $31.10   $31.10  
  Purchase #6 $46.32   11.271%   $51.5407   $51.54   $51.55   $51.50  
  Purchase #7 $101.69   5.322%   $107.1019   $107.10   $107.10   $107.10  
  7 purchase totals = $387.95       $418.6341   $418.62   $418.65   $418.60