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 $61.38   3.202%   $63.3454   $63.35   $63.35   $63.30  
  Purchase #2 $86.81   5.539%   $91.6184   $91.62   $91.60   $91.60  
  Purchase #3 $118.39   11.578%   $132.0972   $132.10   $132.10   $132.10  
  Purchase #4 $202.32   10.724%   $224.0168   $224.02   $224.00   $224.00  
  Purchase #5 $25.58   5.336%   $26.9449   $26.94   $26.95   $26.90  
  Purchase #6 $140.64   7.707%   $151.4791   $151.48   $151.50   $151.50  
  Purchase #7 $205.79   3.366%   $212.7169   $212.72   $212.70   $212.70  
  7 purchase totals = $840.91       $902.2187   $902.23   $902.20   $902.10