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 $227.68   3.451%   $235.5372   $235.54   $235.55   $235.50  
  Purchase #2 $23.97   5.742%   $25.3464   $25.35   $25.35   $25.30  
  Purchase #3 $69.37   5.844%   $73.424   $73.42   $73.40   $73.40  
  Purchase #4 $61.71   11.687%   $68.922   $68.92   $68.90   $68.90  
  Purchase #5 $162.98   7.779%   $175.6582   $175.66   $175.65   $175.70  
  Purchase #6 $25.76   5.438%   $27.1608   $27.16   $27.15   $27.20  
  Purchase #7 $228.42   5.819%   $241.7118   $241.71   $241.70   $241.70  
  7 purchase totals = $799.89       $847.7604   $847.76   $847.70   $847.70