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 $76.52   9.677%   $83.9248   $83.92   $83.90   $83.90  
  Purchase #2 $16.84   7.119%   $18.0388   $18.04   $18.05   $18.00  
  Purchase #3 $60.43   5.357%   $63.6672   $63.67   $63.65   $63.70  
  Purchase #4 $237.79   12.576%   $267.6945   $267.69   $267.70   $267.70  
  Purchase #5 $203.97   5.299%   $214.7784   $214.78   $214.80   $214.80  
  Purchase #6 $244.46   8.408%   $265.0142   $265.01   $265.00   $265.00  
  Purchase #7 $182.48   7.285%   $195.7737   $195.77   $195.75   $195.80  
  7 purchase totals = $1,022.49       $1,108.8916   $1,108.88   $1,108.85   $1,108.90