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 $218.52   9.360%   $238.9735   $238.97   $238.95   $239.00  
  Purchase #2 $70.77   12.518%   $79.629   $79.63   $79.65   $79.60  
  Purchase #3 $36.56   12.217%   $41.0265   $41.03   $41.05   $41.00  
  Purchase #4 $53.92   5.626%   $56.9535   $56.95   $56.95   $57.00  
  Purchase #5 $225.65   12.507%   $253.872   $253.87   $253.85   $253.90  
  Purchase #6 $95.76   5.346%   $100.8793   $100.88   $100.90   $100.90  
  Purchase #7 $239.31   5.662%   $252.8597   $252.86   $252.85   $252.90  
  7 purchase totals = $940.49       $1,024.1935   $1,024.19   $1,024.20   $1,024.30