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 $55.94   4.713%   $58.5765   $58.58   $58.60   $58.60  
  Purchase #2 $145.31   12.635%   $163.6699   $163.67   $163.65   $163.70  
  Purchase #3 $153.35   8.254%   $166.0075   $166.01   $166.00   $166.00  
  Purchase #4 $34.92   12.299%   $39.2148   $39.21   $39.20   $39.20  
  Purchase #5 $26.82   13.587%   $30.464   $30.46   $30.45   $30.50  
  Purchase #6 $135.84   10.117%   $149.5829   $149.58   $149.60   $149.60  
  Purchase #7 $106.41   12.405%   $119.6102   $119.61   $119.60   $119.60  
  7 purchase totals = $658.59       $727.1258   $727.12   $727.10   $727.20