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 $60.64   12.872%   $68.4456   $68.45   $68.45   $68.40  
  Purchase #2 $212.38   11.309%   $236.3981   $236.40   $236.40   $236.40  
  Purchase #3 $187.74   5.306%   $197.7015   $197.70   $197.70   $197.70  
  Purchase #4 $184.77   11.855%   $206.6745   $206.67   $206.65   $206.70  
  Purchase #5 $152.80   10.801%   $169.3039   $169.30   $169.30   $169.30  
  Purchase #6 $181.62   6.262%   $192.993   $192.99   $193.00   $193.00  
  Purchase #7 $246.94   12.317%   $277.3556   $277.36   $277.35   $277.40  
  7 purchase totals = $1,226.89       $1,348.8722   $1,348.87   $1,348.85   $1,348.90