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 $126.77   7.522%   $136.3056   $136.31   $136.30   $136.30  
  Purchase #2 $223.70   9.302%   $244.5086   $244.51   $244.50   $244.50  
  Purchase #3 $154.96   7.387%   $166.4069   $166.41   $166.40   $166.40  
  Purchase #4 $9.29   3.745%   $9.6379   $9.64   $9.65   $9.60  
  Purchase #5 $144.35   7.317%   $154.9121   $154.91   $154.90   $154.90  
  Purchase #6 $226.57   13.136%   $256.3322   $256.33   $256.35   $256.30  
  Purchase #7 $58.67   10.419%   $64.7828   $64.78   $64.80   $64.80  
  7 purchase totals = $944.31       $1,032.8861   $1,032.89   $1,032.90   $1,032.80