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 $128.25   11.428%   $142.9064   $142.91   $142.90   $142.90  
  Purchase #2 $79.70   12.199%   $89.4226   $89.42   $89.40   $89.40  
  Purchase #3 $140.28   5.148%   $147.5016   $147.50   $147.50   $147.50  
  Purchase #4 $7.37   8.113%   $7.9679   $7.97   $7.95   $8.00  
  Purchase #5 $10.82   13.813%   $12.3146   $12.31   $12.30   $12.30  
  Purchase #6 $212.80   7.116%   $227.9428   $227.94   $227.95   $227.90  
  Purchase #7 $94.68   3.371%   $97.8717   $97.87   $97.85   $97.90  
  7 purchase totals = $673.90       $725.9276   $725.92   $725.85   $725.90