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 $68.48   10.656%   $75.7772   $75.78   $75.80   $75.80  
  Purchase #2 $137.55   7.694%   $148.1331   $148.13   $148.15   $148.10  
  Purchase #3 $72.69   5.709%   $76.8399   $76.84   $76.85   $76.80  
  Purchase #4 $225.46   5.483%   $237.822   $237.82   $237.80   $237.80  
  Purchase #5 $50.29   6.324%   $53.4703   $53.47   $53.45   $53.50  
  Purchase #6 $61.28   6.641%   $65.3496   $65.35   $65.35   $65.30  
  Purchase #7 $121.44   11.707%   $135.657   $135.66   $135.65   $135.70  
  7 purchase totals = $737.19       $793.0491   $793.05   $793.05   $793.00