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 $134.81   12.457%   $151.6033   $151.60   $151.60   $151.60  
  Purchase #2 $80.97   3.652%   $83.927   $83.93   $83.95   $83.90  
  Purchase #3 $22.63   13.469%   $25.678   $25.68   $25.70   $25.70  
  Purchase #4 $138.29   3.574%   $143.2325   $143.23   $143.25   $143.20  
  Purchase #5 $97.40   3.618%   $100.9239   $100.92   $100.90   $100.90  
  Purchase #6 $202.65   7.435%   $217.717   $217.72   $217.70   $217.70  
  Purchase #7 $162.45   5.774%   $171.8299   $171.83   $171.85   $171.80  
  7 purchase totals = $839.20       $894.9116   $894.91   $894.95   $894.80