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 $65.56   11.656%   $73.2017   $73.20   $73.20   $73.20  
  Purchase #2 $63.97   13.379%   $72.5285   $72.53   $72.55   $72.50  
  Purchase #3 $50.43   13.639%   $57.3081   $57.31   $57.30   $57.30  
  Purchase #4 $217.65   4.184%   $226.7565   $226.76   $226.75   $226.80  
  Purchase #5 $138.45   6.486%   $147.4299   $147.43   $147.45   $147.40  
  Purchase #6 $12.93   8.263%   $13.9984   $14.00   $14.00   $14.00  
  Purchase #7 $204.75   10.290%   $225.8188   $225.82   $225.80   $225.80  
  7 purchase totals = $753.74       $817.0419   $817.05   $817.05   $817.00