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 $64.66   13.144%   $73.1589   $73.16   $73.15   $73.20  
  Purchase #2 $105.73   12.597%   $119.0488   $119.05   $119.05   $119.00  
  Purchase #3 $49.29   13.408%   $55.8988   $55.90   $55.90   $55.90  
  Purchase #4 $138.36   5.651%   $146.1787   $146.18   $146.20   $146.20  
  Purchase #5 $46.61   12.735%   $52.5458   $52.55   $52.55   $52.50  
  Purchase #6 $145.34   4.454%   $151.8134   $151.81   $151.80   $151.80  
  Purchase #7 $181.84   6.656%   $193.9433   $193.94   $193.95   $193.90  
  7 purchase totals = $731.83       $792.5877   $792.59   $792.60   $792.50