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 $54.98   12.374%   $61.7832   $61.78   $61.80   $61.80  
  Purchase #2 $195.80   5.202%   $205.9855   $205.99   $206.00   $206.00  
  Purchase #3 $85.83   5.570%   $90.6107   $90.61   $90.60   $90.60  
  Purchase #4 $224.57   8.303%   $243.216   $243.22   $243.20   $243.20  
  Purchase #5 $16.82   3.792%   $17.4578   $17.46   $17.45   $17.50  
  Purchase #6 $91.43   5.263%   $96.242   $96.24   $96.25   $96.20  
  Purchase #7 $70.57   9.269%   $77.1111   $77.11   $77.10   $77.10  
  7 purchase totals = $740.00       $792.4063   $792.41   $792.40   $792.40