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 $217.44   7.815%   $234.4329   $234.43   $234.45   $234.40  
  Purchase #2 $44.79   4.182%   $46.6631   $46.66   $46.65   $46.70  
  Purchase #3 $202.56   8.129%   $219.0261   $219.03   $219.05   $219.00  
  Purchase #4 $114.93   5.447%   $121.1902   $121.19   $121.20   $121.20  
  Purchase #5 $125.60   4.662%   $131.4555   $131.46   $131.45   $131.50  
  Purchase #6 $133.45   9.266%   $145.8155   $145.82   $145.80   $145.80  
  Purchase #7 $91.67   3.636%   $95.0031   $95.00   $95.00   $95.00  
  7 purchase totals = $930.44       $993.5864   $993.59   $993.60   $993.60