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 $218.50   7.685%   $235.2917   $235.29   $235.30   $235.30  
  Purchase #2 $24.57   5.750%   $25.9828   $25.98   $26.00   $26.00  
  Purchase #3 $67.42   3.237%   $69.6024   $69.60   $69.60   $69.60  
  Purchase #4 $106.91   3.210%   $110.3418   $110.34   $110.35   $110.30  
  Purchase #5 $42.70   11.770%   $47.7258   $47.73   $47.75   $47.70  
  Purchase #6 $204.69   10.369%   $225.9143   $225.91   $225.90   $225.90  
  Purchase #7 $17.32   11.188%   $19.2578   $19.26   $19.25   $19.30  
  7 purchase totals = $682.11       $734.1166   $734.11   $734.15   $734.10