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 $227.67   8.193%   $246.323   $246.32   $246.30   $246.30  
  Purchase #2 $88.31   7.513%   $94.9447   $94.94   $94.95   $94.90  
  Purchase #3 $59.48   12.581%   $66.9632   $66.96   $66.95   $67.00  
  Purchase #4 $250.76   5.120%   $263.5989   $263.60   $263.60   $263.60  
  Purchase #5 $7.33   3.706%   $7.6016   $7.60   $7.60   $7.60  
  Purchase #6 $184.28   9.331%   $201.4752   $201.48   $201.50   $201.50  
  Purchase #7 $134.46   12.846%   $151.7327   $151.73   $151.75   $151.70  
  7 purchase totals = $952.29       $1,032.6393   $1,032.63   $1,032.65   $1,032.60