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 $236.54   11.302%   $263.2738   $263.27   $263.25   $263.30  
  Purchase #2 $247.47   6.544%   $263.6644   $263.66   $263.65   $263.70  
  Purchase #3 $232.81   8.201%   $251.9027   $251.90   $251.90   $251.90  
  Purchase #4 $112.68   12.399%   $126.6512   $126.65   $126.65   $126.70  
  Purchase #5 $172.81   10.585%   $191.1019   $191.10   $191.10   $191.10  
  Purchase #6 $157.98   6.452%   $168.1729   $168.17   $168.15   $168.20  
  Purchase #7 $83.29   10.349%   $91.9097   $91.91   $91.90   $91.90  
  7 purchase totals = $1,243.58       $1,356.6766   $1,356.66   $1,356.60   $1,356.80