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 $119.77   10.751%   $132.6465   $132.65   $132.65   $132.60  
  Purchase #2 $132.57   8.351%   $143.6409   $143.64   $143.65   $143.60  
  Purchase #3 $204.42   9.229%   $223.2859   $223.29   $223.30   $223.30  
  Purchase #4 $217.35   4.346%   $226.796   $226.80   $226.80   $226.80  
  Purchase #5 $26.40   9.570%   $28.9265   $28.93   $28.95   $28.90  
  Purchase #6 $109.71   8.851%   $119.4204   $119.42   $119.40   $119.40  
  Purchase #7 $146.73   13.356%   $166.3273   $166.33   $166.35   $166.30  
  7 purchase totals = $956.95       $1,041.0435   $1,041.06   $1,041.10   $1,040.90