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 $98.50   11.259%   $109.5901   $109.59   $109.60   $109.60  
  Purchase #2 $15.64   7.331%   $16.7866   $16.79   $16.80   $16.80  
  Purchase #3 $107.78   9.244%   $117.7432   $117.74   $117.75   $117.70  
  Purchase #4 $211.43   3.287%   $218.3797   $218.38   $218.40   $218.40  
  Purchase #5 $95.98   12.859%   $108.3221   $108.32   $108.30   $108.30  
  Purchase #6 $203.51   3.784%   $211.2108   $211.21   $211.20   $211.20  
  Purchase #7 $151.89   4.207%   $158.28   $158.28   $158.30   $158.30  
  7 purchase totals = $884.73       $940.3125   $940.31   $940.35   $940.30