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 $87.92   7.503%   $94.5166   $94.52   $94.50   $94.50  
  Purchase #2 $192.32   9.481%   $210.5539   $210.55   $210.55   $210.60  
  Purchase #3 $62.28   10.533%   $68.84   $68.84   $68.85   $68.80  
  Purchase #4 $156.50   7.516%   $168.2625   $168.26   $168.25   $168.30  
  Purchase #5 $213.68   10.189%   $235.4519   $235.45   $235.45   $235.50  
  Purchase #6 $84.53   4.406%   $88.2544   $88.25   $88.25   $88.30  
  Purchase #7 $107.28   5.468%   $113.1461   $113.15   $113.15   $113.10  
  7 purchase totals = $904.51       $979.0254   $979.02   $979.00   $979.10