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 $183.98   10.149%   $202.6521   $202.65   $202.65   $202.70  
  Purchase #2 $87.76   5.690%   $92.7535   $92.75   $92.75   $92.80  
  Purchase #3 $129.37   10.768%   $143.3006   $143.30   $143.30   $143.30  
  Purchase #4 $242.91   11.692%   $271.311   $271.31   $271.30   $271.30  
  Purchase #5 $15.40   7.735%   $16.5912   $16.59   $16.60   $16.60  
  Purchase #6 $216.80   3.866%   $225.1815   $225.18   $225.20   $225.20  
  Purchase #7 $76.82   4.721%   $80.4467   $80.45   $80.45   $80.40  
  7 purchase totals = $953.04       $1,032.2366   $1,032.23   $1,032.25   $1,032.30