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 $232.75   5.576%   $245.7281   $245.73   $245.75   $245.70  
  Purchase #2 $29.97   12.244%   $33.6395   $33.64   $33.65   $33.60  
  Purchase #3 $24.77   5.677%   $26.1762   $26.18   $26.20   $26.20  
  Purchase #4 $5.61   7.464%   $6.0287   $6.03   $6.05   $6.00  
  Purchase #5 $57.78   3.114%   $59.5793   $59.58   $59.60   $59.60  
  Purchase #6 $234.46   7.685%   $252.4783   $252.48   $252.50   $252.50  
  Purchase #7 $169.45   12.647%   $190.8803   $190.88   $190.90   $190.90  
  7 purchase totals = $754.79       $814.5104   $814.52   $814.65   $814.50