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 $87.51   7.147%   $93.7643   $93.76   $93.75   $93.80  
  Purchase #2 $209.58   11.770%   $234.2476   $234.25   $234.25   $234.20  
  Purchase #3 $198.68   10.377%   $219.297   $219.30   $219.30   $219.30  
  Purchase #4 $5.96   4.281%   $6.2151   $6.22   $6.20   $6.20  
  Purchase #5 $250.76   11.445%   $279.4595   $279.46   $279.45   $279.50  
  Purchase #6 $131.93   5.552%   $139.2548   $139.25   $139.25   $139.30  
  Purchase #7 $101.84   10.552%   $112.5862   $112.59   $112.60   $112.60  
  7 purchase totals = $986.26       $1,084.8245   $1,084.83   $1,084.80   $1,084.90