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 $76.38   11.723%   $85.334   $85.33   $85.35   $85.30  
  Purchase #2 $49.45   10.541%   $54.6625   $54.66   $54.65   $54.70  
  Purchase #3 $138.98   13.385%   $157.5825   $157.58   $157.60   $157.60  
  Purchase #4 $24.44   11.465%   $27.242   $27.24   $27.25   $27.20  
  Purchase #5 $67.71   11.398%   $75.4276   $75.43   $75.45   $75.40  
  Purchase #6 $168.59   3.425%   $174.3642   $174.36   $174.35   $174.40  
  Purchase #7 $181.63   9.767%   $199.3698   $199.37   $199.35   $199.40  
  7 purchase totals = $707.18       $773.9826   $773.97   $774.00   $774.00