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 $27.84   6.850%   $29.747   $29.75   $29.75   $29.70  
  Purchase #2 $167.95   5.786%   $177.6676   $177.67   $177.65   $177.70  
  Purchase #3 $236.72   7.558%   $254.6113   $254.61   $254.60   $254.60  
  Purchase #4 $20.55   9.462%   $22.4944   $22.49   $22.50   $22.50  
  Purchase #5 $60.42   5.192%   $63.557   $63.56   $63.55   $63.60  
  Purchase #6 $183.46   11.203%   $204.013   $204.01   $204.00   $204.00  
  Purchase #7 $237.49   13.474%   $269.4894   $269.49   $269.50   $269.50  
  7 purchase totals = $934.43       $1,021.5797   $1,021.58   $1,021.55   $1,021.60