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 $134.80   13.484%   $152.9764   $152.98   $153.00   $153.00  
  Purchase #2 $23.34   6.784%   $24.9234   $24.92   $24.90   $24.90  
  Purchase #3 $151.83   13.472%   $172.2845   $172.28   $172.30   $172.30  
  Purchase #4 $58.77   13.254%   $66.5594   $66.56   $66.55   $66.60  
  Purchase #5 $238.30   4.536%   $249.1093   $249.11   $249.10   $249.10  
  Purchase #6 $187.38   8.331%   $202.9906   $202.99   $203.00   $203.00  
  Purchase #7 $226.99   13.293%   $257.1638   $257.16   $257.15   $257.20  
  7 purchase totals = $1,021.41       $1,126.0074   $1,126.00   $1,126.00   $1,126.10