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 $119.99   11.691%   $134.018   $134.02   $134.00   $134.00  
  Purchase #2 $88.59   6.124%   $94.0153   $94.02   $94.00   $94.00  
  Purchase #3 $73.29   7.438%   $78.7413   $78.74   $78.75   $78.70  
  Purchase #4 $21.64   6.232%   $22.9886   $22.99   $23.00   $23.00  
  Purchase #5 $110.96   4.489%   $115.941   $115.94   $115.95   $115.90  
  Purchase #6 $237.99   7.833%   $256.6318   $256.63   $256.65   $256.60  
  Purchase #7 $146.65   10.597%   $162.1905   $162.19   $162.20   $162.20  
  7 purchase totals = $799.11       $864.5265   $864.53   $864.55   $864.40