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 $234.62   5.399%   $247.2871   $247.29   $247.30   $247.30  
  Purchase #2 $107.48   10.174%   $118.415   $118.42   $118.40   $118.40  
  Purchase #3 $167.94   10.869%   $186.1934   $186.19   $186.20   $186.20  
  Purchase #4 $168.60   6.322%   $179.2589   $179.26   $179.25   $179.30  
  Purchase #5 $206.43   8.695%   $224.3791   $224.38   $224.40   $224.40  
  Purchase #6 $137.73   4.666%   $144.1565   $144.16   $144.15   $144.20  
  Purchase #7 $85.81   7.183%   $91.9737   $91.97   $91.95   $92.00  
  7 purchase totals = $1,108.61       $1,191.6637   $1,191.67   $1,191.65   $1,191.80