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 $112.61   12.580%   $126.7763   $126.78   $126.80   $126.80  
  Purchase #2 $141.93   13.150%   $160.5938   $160.59   $160.60   $160.60  
  Purchase #3 $213.45   12.618%   $240.3831   $240.38   $240.40   $240.40  
  Purchase #4 $126.89   9.382%   $138.7948   $138.79   $138.80   $138.80  
  Purchase #5 $88.77   3.250%   $91.655   $91.66   $91.65   $91.70  
  Purchase #6 $115.30   13.719%   $131.118   $131.12   $131.10   $131.10  
  Purchase #7 $183.41   5.570%   $193.6259   $193.63   $193.65   $193.60  
  7 purchase totals = $982.36       $1,082.9469   $1,082.95   $1,083.00   $1,083.00