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 $59.26   3.516%   $61.3436   $61.34   $61.35   $61.30  
  Purchase #2 $11.43   13.801%   $13.0075   $13.01   $13.00   $13.00  
  Purchase #3 $42.32   11.833%   $47.3277   $47.33   $47.35   $47.30  
  Purchase #4 $210.29   5.615%   $222.0978   $222.10   $222.10   $222.10  
  Purchase #5 $56.47   7.607%   $60.7657   $60.77   $60.75   $60.80  
  Purchase #6 $221.91   7.358%   $238.2381   $238.24   $238.25   $238.20  
  Purchase #7 $61.87   3.804%   $64.2235   $64.22   $64.20   $64.20  
  7 purchase totals = $663.55       $707.0039   $707.01   $707.00   $706.90