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 $232.77   11.287%   $259.0427   $259.04   $259.05   $259.00  
  Purchase #2 $182.80   7.541%   $196.5849   $196.58   $196.60   $196.60  
  Purchase #3 $31.34   10.215%   $34.5414   $34.54   $34.55   $34.50  
  Purchase #4 $59.39   4.717%   $62.1914   $62.19   $62.20   $62.20  
  Purchase #5 $26.69   10.586%   $29.5154   $29.52   $29.50   $29.50  
  Purchase #6 $250.60   12.845%   $282.7896   $282.79   $282.80   $282.80  
  Purchase #7 $170.42   13.386%   $193.2324   $193.23   $193.25   $193.20  
  7 purchase totals = $954.01       $1,057.8978   $1,057.89   $1,057.95   $1,057.80