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 $98.57   3.384%   $101.9056   $101.91   $101.90   $101.90  
  Purchase #2 $136.44   11.375%   $151.9601   $151.96   $151.95   $152.00  
  Purchase #3 $17.27   3.292%   $17.8385   $17.84   $17.85   $17.80  
  Purchase #4 $207.62   13.606%   $235.8688   $235.87   $235.85   $235.90  
  Purchase #5 $86.26   9.592%   $94.5341   $94.53   $94.55   $94.50  
  Purchase #6 $54.92   9.363%   $60.0622   $60.06   $60.05   $60.10  
  Purchase #7 $89.90   11.399%   $100.1477   $100.15   $100.15   $100.10  
  7 purchase totals = $690.98       $762.3170   $762.32   $762.30   $762.30