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 $228.39   13.847%   $260.0152   $260.02   $260.00   $260.00  
  Purchase #2 $107.76   9.658%   $118.1675   $118.17   $118.15   $118.20  
  Purchase #3 $207.34   8.336%   $224.6239   $224.62   $224.60   $224.60  
  Purchase #4 $211.72   8.519%   $229.7564   $229.76   $229.75   $229.80  
  Purchase #5 $55.29   13.219%   $62.5988   $62.60   $62.60   $62.60  
  Purchase #6 $87.54   6.450%   $93.1863   $93.19   $93.20   $93.20  
  Purchase #7 $172.86   3.322%   $178.6024   $178.60   $178.60   $178.60  
  7 purchase totals = $1,070.90       $1,166.9505   $1,166.96   $1,166.90   $1,167.00