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 $85.72   10.645%   $94.8449   $94.84   $94.85   $94.80  
  Purchase #2 $216.26   11.419%   $240.9547   $240.95   $240.95   $241.00  
  Purchase #3 $25.94   13.135%   $29.3472   $29.35   $29.35   $29.30  
  Purchase #4 $224.72   10.307%   $247.8819   $247.88   $247.90   $247.90  
  Purchase #5 $68.45   5.190%   $72.0026   $72.00   $72.00   $72.00  
  Purchase #6 $106.31   5.681%   $112.3495   $112.35   $112.35   $112.30  
  Purchase #7 $121.42   10.833%   $134.5734   $134.57   $134.55   $134.60  
  7 purchase totals = $848.82       $931.9542   $931.94   $931.95   $931.90