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 $212.63   13.613%   $241.5753   $241.58   $241.60   $241.60  
  Purchase #2 $67.86   12.737%   $76.5033   $76.50   $76.50   $76.50  
  Purchase #3 $89.55   5.203%   $94.2093   $94.21   $94.20   $94.20  
  Purchase #4 $123.39   4.287%   $128.6797   $128.68   $128.70   $128.70  
  Purchase #5 $180.50   12.345%   $202.7827   $202.78   $202.80   $202.80  
  Purchase #6 $123.89   8.661%   $134.6201   $134.62   $134.60   $134.60  
  Purchase #7 $129.98   11.714%   $145.2059   $145.21   $145.20   $145.20  
  7 purchase totals = $927.80       $1,023.5763   $1,023.58   $1,023.60   $1,023.60