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 $150.73   9.226%   $164.6363   $164.64   $164.65   $164.60  
  Purchase #2 $211.43   7.311%   $226.8876   $226.89   $226.90   $226.90  
  Purchase #3 $86.66   7.637%   $93.2782   $93.28   $93.30   $93.30  
  Purchase #4 $241.44   4.865%   $253.1861   $253.19   $253.20   $253.20  
  Purchase #5 $93.68   4.820%   $98.1954   $98.20   $98.20   $98.20  
  Purchase #6 $37.56   6.396%   $39.9623   $39.96   $39.95   $40.00  
  Purchase #7 $202.84   12.556%   $228.3086   $228.31   $228.30   $228.30  
  7 purchase totals = $1,024.34       $1,104.4545   $1,104.47   $1,104.50   $1,104.50