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 $182.51   11.754%   $203.9622   $203.96   $203.95   $204.00  
  Purchase #2 $242.80   9.477%   $265.8102   $265.81   $265.80   $265.80  
  Purchase #3 $126.49   9.832%   $138.9265   $138.93   $138.95   $138.90  
  Purchase #4 $15.78   7.360%   $16.9414   $16.94   $16.95   $16.90  
  Purchase #5 $157.94   11.135%   $175.5266   $175.53   $175.55   $175.50  
  Purchase #6 $156.73   6.347%   $166.6777   $166.68   $166.70   $166.70  
  Purchase #7 $166.47   11.571%   $185.7322   $185.73   $185.75   $185.70  
  7 purchase totals = $1,048.72       $1,153.5768   $1,153.58   $1,153.65   $1,153.50