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 $91.56   3.606%   $94.8617   $94.86   $94.85   $94.90  
  Purchase #2 $8.46   10.199%   $9.3228   $9.32   $9.30   $9.30  
  Purchase #3 $196.49   9.208%   $214.5828   $214.58   $214.60   $214.60  
  Purchase #4 $48.82   11.565%   $54.466   $54.47   $54.45   $54.50  
  Purchase #5 $185.78   9.187%   $202.8476   $202.85   $202.85   $202.80  
  Purchase #6 $157.58   6.164%   $167.2932   $167.29   $167.30   $167.30  
  Purchase #7 $190.42   7.302%   $204.3245   $204.32   $204.30   $204.30  
  7 purchase totals = $879.11       $947.6986   $947.69   $947.65   $947.70