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 $114.50   11.561%   $127.7373   $127.74   $127.75   $127.70  
  Purchase #2 $144.92   13.555%   $164.5639   $164.56   $164.55   $164.60  
  Purchase #3 $44.80   7.473%   $48.1479   $48.15   $48.15   $48.10  
  Purchase #4 $207.50   8.797%   $225.7538   $225.75   $225.75   $225.80  
  Purchase #5 $27.99   4.769%   $29.3248   $29.32   $29.30   $29.30  
  Purchase #6 $149.91   10.384%   $165.4767   $165.48   $165.50   $165.50  
  Purchase #7 $11.57   3.451%   $11.9693   $11.97   $11.95   $12.00  
  7 purchase totals = $701.19       $772.9737   $772.97   $772.95   $773.00