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 $212.28   11.474%   $236.637   $236.64   $236.65   $236.60  
  Purchase #2 $160.53   12.353%   $180.3603   $180.36   $180.35   $180.40  
  Purchase #3 $243.96   9.240%   $266.5019   $266.50   $266.50   $266.50  
  Purchase #4 $185.34   13.818%   $210.9503   $210.95   $210.95   $211.00  
  Purchase #5 $199.81   12.626%   $225.038   $225.04   $225.05   $225.00  
  Purchase #6 $33.31   4.579%   $34.8353   $34.84   $34.85   $34.80  
  Purchase #7 $118.30   6.243%   $125.6855   $125.69   $125.70   $125.70  
  7 purchase totals = $1,153.53       $1,280.0083   $1,280.02   $1,280.05   $1,280.00