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 $194.60   13.228%   $220.3417   $220.34   $220.35   $220.30  
  Purchase #2 $232.53   7.213%   $249.3024   $249.30   $249.30   $249.30  
  Purchase #3 $78.61   12.722%   $88.6108   $88.61   $88.60   $88.60  
  Purchase #4 $202.82   12.831%   $228.8438   $228.84   $228.85   $228.80  
  Purchase #5 $195.76   9.329%   $214.0225   $214.02   $214.00   $214.00  
  Purchase #6 $179.69   13.367%   $203.7092   $203.71   $203.70   $203.70  
  Purchase #7 $65.95   10.676%   $72.9908   $72.99   $73.00   $73.00  
  7 purchase totals = $1,149.96       $1,277.8212   $1,277.81   $1,277.80   $1,277.70