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 $62.28   13.108%   $70.4437   $70.44   $70.45   $70.40  
  Purchase #2 $44.34   3.201%   $45.7593   $45.76   $45.75   $45.80  
  Purchase #3 $217.94   9.231%   $238.058   $238.06   $238.05   $238.10  
  Purchase #4 $170.78   10.390%   $188.524   $188.52   $188.50   $188.50  
  Purchase #5 $239.55   10.515%   $264.7387   $264.74   $264.75   $264.70  
  Purchase #6 $73.79   4.367%   $77.0124   $77.01   $77.00   $77.00  
  Purchase #7 $66.99   13.137%   $75.7905   $75.79   $75.80   $75.80  
  7 purchase totals = $875.67       $960.3266   $960.32   $960.30   $960.30