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 $156.85   6.814%   $167.5378   $167.54   $167.55   $167.50  
  Purchase #2 $181.39   11.312%   $201.9088   $201.91   $201.90   $201.90  
  Purchase #3 $97.36   12.752%   $109.7753   $109.78   $109.80   $109.80  
  Purchase #4 $229.94   5.591%   $242.7959   $242.80   $242.80   $242.80  
  Purchase #5 $39.32   8.718%   $42.7479   $42.75   $42.75   $42.70  
  Purchase #6 $32.79   13.300%   $37.1511   $37.15   $37.15   $37.20  
  Purchase #7 $22.54   4.555%   $23.5667   $23.57   $23.55   $23.60  
  7 purchase totals = $760.19       $825.4835   $825.50   $825.50   $825.50