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 $83.33   12.262%   $93.5479   $93.55   $93.55   $93.50  
  Purchase #2 $240.52   8.580%   $261.1566   $261.16   $261.15   $261.20  
  Purchase #3 $82.35   12.220%   $92.4132   $92.41   $92.40   $92.40  
  Purchase #4 $161.65   10.751%   $179.029   $179.03   $179.05   $179.00  
  Purchase #5 $59.67   6.189%   $63.363   $63.36   $63.35   $63.40  
  Purchase #6 $185.33   9.618%   $203.155   $203.16   $203.15   $203.20  
  Purchase #7 $174.73   8.601%   $189.7585   $189.76   $189.75   $189.80  
  7 purchase totals = $987.58       $1,082.4232   $1,082.43   $1,082.40   $1,082.50