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 $207.41   12.222%   $232.7597   $232.76   $232.75   $232.80  
  Purchase #2 $249.30   7.748%   $268.6158   $268.62   $268.60   $268.60  
  Purchase #3 $72.43   4.131%   $75.4221   $75.42   $75.40   $75.40  
  Purchase #4 $63.93   6.492%   $68.0803   $68.08   $68.10   $68.10  
  Purchase #5 $247.26   6.372%   $263.0154   $263.02   $263.00   $263.00  
  Purchase #6 $224.82   6.843%   $240.2044   $240.20   $240.20   $240.20  
  Purchase #7 $206.28   4.338%   $215.2284   $215.23   $215.25   $215.20  
  7 purchase totals = $1,271.43       $1,363.3261   $1,363.33   $1,363.30   $1,363.30