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 $160.54   8.300%   $173.8648   $173.86   $173.85   $173.90  
  Purchase #2 $28.94   11.264%   $32.1998   $32.20   $32.20   $32.20  
  Purchase #3 $43.86   4.503%   $45.835   $45.84   $45.85   $45.80  
  Purchase #4 $64.92   5.375%   $68.4095   $68.41   $68.40   $68.40  
  Purchase #5 $121.38   6.652%   $129.4542   $129.45   $129.45   $129.50  
  Purchase #6 $90.94   5.810%   $96.2236   $96.22   $96.20   $96.20  
  Purchase #7 $110.51   12.352%   $124.1602   $124.16   $124.15   $124.20  
  7 purchase totals = $621.09       $670.1471   $670.14   $670.10   $670.20