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 $88.90   9.113%   $97.0015   $97.00   $97.00   $97.00  
  Purchase #2 $225.69   6.689%   $240.7864   $240.79   $240.80   $240.80  
  Purchase #3 $166.26   3.714%   $172.4349   $172.43   $172.45   $172.40  
  Purchase #4 $106.74   6.787%   $113.9844   $113.98   $114.00   $114.00  
  Purchase #5 $20.76   4.409%   $21.6753   $21.68   $21.70   $21.70  
  Purchase #6 $239.88   9.809%   $263.4098   $263.41   $263.40   $263.40  
  Purchase #7 $119.92   4.659%   $125.5071   $125.51   $125.50   $125.50  
  7 purchase totals = $968.15       $1,034.7994   $1,034.80   $1,034.85   $1,034.80