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 $182.46   11.783%   $203.9593   $203.96   $203.95   $204.00  
  Purchase #2 $178.47   6.198%   $189.5316   $189.53   $189.55   $189.50  
  Purchase #3 $49.28   7.167%   $52.8119   $52.81   $52.80   $52.80  
  Purchase #4 $103.84   3.525%   $107.5004   $107.50   $107.50   $107.50  
  Purchase #5 $20.51   5.157%   $21.5677   $21.57   $21.55   $21.60  
  Purchase #6 $162.96   10.272%   $179.6993   $179.70   $179.70   $179.70  
  Purchase #7 $133.57   12.693%   $150.524   $150.52   $150.50   $150.50  
  7 purchase totals = $831.09       $905.5942   $905.59   $905.55   $905.60