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 $92.73   11.561%   $103.4505   $103.45   $103.45   $103.50  
  Purchase #2 $158.28   6.562%   $168.6663   $168.67   $168.65   $168.70  
  Purchase #3 $178.44   7.439%   $191.7142   $191.71   $191.70   $191.70  
  Purchase #4 $157.52   13.638%   $179.0026   $179.00   $179.00   $179.00  
  Purchase #5 $111.99   6.681%   $119.4721   $119.47   $119.45   $119.50  
  Purchase #6 $159.79   10.410%   $176.4241   $176.42   $176.40   $176.40  
  Purchase #7 $95.93   12.505%   $107.926   $107.93   $107.95   $107.90  
  7 purchase totals = $954.68       $1,046.6558   $1,046.65   $1,046.60   $1,046.70