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 $148.45   10.221%   $163.6231   $163.62   $163.60   $163.60  
  Purchase #2 $141.71   9.276%   $154.855   $154.86   $154.85   $154.90  
  Purchase #3 $74.71   13.274%   $84.627   $84.63   $84.65   $84.60  
  Purchase #4 $190.28   3.413%   $196.7743   $196.77   $196.75   $196.80  
  Purchase #5 $240.27   11.591%   $268.1197   $268.12   $268.10   $268.10  
  Purchase #6 $188.81   8.774%   $205.3762   $205.38   $205.40   $205.40  
  Purchase #7 $69.78   7.454%   $74.9814   $74.98   $75.00   $75.00  
  7 purchase totals = $1,054.01       $1,148.3567   $1,148.36   $1,148.35   $1,148.40