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 $216.93   11.850%   $242.6362   $242.64   $242.65   $242.60  
  Purchase #2 $121.70   5.817%   $128.7793   $128.78   $128.80   $128.80  
  Purchase #3 $73.80   11.771%   $82.487   $82.49   $82.50   $82.50  
  Purchase #4 $41.71   9.158%   $45.5298   $45.53   $45.55   $45.50  
  Purchase #5 $191.32   5.521%   $201.8828   $201.88   $201.90   $201.90  
  Purchase #6 $192.40   10.375%   $212.3615   $212.36   $212.35   $212.40  
  Purchase #7 $44.40   11.853%   $49.6627   $49.66   $49.65   $49.70  
  7 purchase totals = $882.26       $963.3393   $963.34   $963.40   $963.40