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 $50.46   6.272%   $53.6249   $53.62   $53.60   $53.60  
  Purchase #2 $150.55   4.523%   $157.3594   $157.36   $157.35   $157.40  
  Purchase #3 $205.57   10.290%   $226.7232   $226.72   $226.70   $226.70  
  Purchase #4 $51.84   5.808%   $54.8509   $54.85   $54.85   $54.90  
  Purchase #5 $73.32   11.793%   $81.9666   $81.97   $81.95   $82.00  
  Purchase #6 $126.84   10.395%   $140.025   $140.03   $140.05   $140.00  
  Purchase #7 $37.31   10.300%   $41.1529   $41.15   $41.15   $41.20  
  7 purchase totals = $695.89       $755.7029   $755.70   $755.65   $755.80