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 $201.59   7.280%   $216.2658   $216.27   $216.25   $216.30  
  Purchase #2 $196.77   11.117%   $218.6449   $218.64   $218.65   $218.60  
  Purchase #3 $17.68   12.281%   $19.8513   $19.85   $19.85   $19.90  
  Purchase #4 $158.54   7.360%   $170.2085   $170.21   $170.20   $170.20  
  Purchase #5 $141.78   12.646%   $159.7095   $159.71   $159.70   $159.70  
  Purchase #6 $65.43   6.711%   $69.821   $69.82   $69.80   $69.80  
  Purchase #7 $246.42   12.417%   $277.018   $277.02   $277.00   $277.00  
  7 purchase totals = $1,028.21       $1,131.5190   $1,131.52   $1,131.45   $1,131.50