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 $194.27   6.386%   $206.6761   $206.68   $206.70   $206.70  
  Purchase #2 $184.34   4.343%   $192.3459   $192.35   $192.35   $192.30  
  Purchase #3 $77.29   4.486%   $80.7572   $80.76   $80.75   $80.80  
  Purchase #4 $67.56   12.468%   $75.9834   $75.98   $76.00   $76.00  
  Purchase #5 $68.77   5.577%   $72.6053   $72.61   $72.60   $72.60  
  Purchase #6 $225.83   10.375%   $249.2599   $249.26   $249.25   $249.30  
  Purchase #7 $165.56   10.707%   $183.2865   $183.29   $183.30   $183.30  
  7 purchase totals = $983.62       $1,060.9143   $1,060.93   $1,060.95   $1,061.00