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 $64.79   4.369%   $67.6207   $67.62   $67.60   $67.60  
  Purchase #2 $10.66   9.697%   $11.6937   $11.69   $11.70   $11.70  
  Purchase #3 $102.26   12.709%   $115.2562   $115.26   $115.25   $115.30  
  Purchase #4 $30.79   8.428%   $33.385   $33.39   $33.40   $33.40  
  Purchase #5 $77.56   9.190%   $84.6878   $84.69   $84.70   $84.70  
  Purchase #6 $14.74   12.349%   $16.5602   $16.56   $16.55   $16.60  
  Purchase #7 $185.75   4.331%   $193.7948   $193.79   $193.80   $193.80  
  7 purchase totals = $486.55       $522.9984   $523.00   $523.00   $523.10