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 $154.94   12.719%   $174.6468   $174.65   $174.65   $174.60  
  Purchase #2 $10.35   13.654%   $11.7632   $11.76   $11.75   $11.80  
  Purchase #3 $187.64   7.709%   $202.1052   $202.11   $202.10   $202.10  
  Purchase #4 $141.47   4.150%   $147.341   $147.34   $147.35   $147.30  
  Purchase #5 $104.94   11.357%   $116.858   $116.86   $116.85   $116.90  
  Purchase #6 $151.47   13.507%   $171.9291   $171.93   $171.95   $171.90  
  Purchase #7 $120.32   4.197%   $125.3698   $125.37   $125.35   $125.40  
  7 purchase totals = $871.13       $950.0131   $950.02   $950.00   $950.00