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 $241.98   9.312%   $264.5132   $264.51   $264.50   $264.50  
  Purchase #2 $37.99   4.165%   $39.5723   $39.57   $39.55   $39.60  
  Purchase #3 $160.32   4.422%   $167.4094   $167.41   $167.40   $167.40  
  Purchase #4 $247.58   11.460%   $275.9527   $275.95   $275.95   $276.00  
  Purchase #5 $79.87   13.831%   $90.9168   $90.92   $90.90   $90.90  
  Purchase #6 $186.55   8.319%   $202.0691   $202.07   $202.05   $202.10  
  Purchase #7 $113.94   4.708%   $119.3043   $119.30   $119.30   $119.30  
  7 purchase totals = $1,068.23       $1,159.7378   $1,159.73   $1,159.65   $1,159.80