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 $137.64   11.191%   $153.0433   $153.04   $153.05   $153.00  
  Purchase #2 $59.33   5.597%   $62.6507   $62.65   $62.65   $62.70  
  Purchase #3 $189.57   3.271%   $195.7708   $195.77   $195.75   $195.80  
  Purchase #4 $233.98   8.753%   $254.4603   $254.46   $254.45   $254.50  
  Purchase #5 $242.61   9.623%   $265.9564   $265.96   $265.95   $266.00  
  Purchase #6 $246.84   7.833%   $266.175   $266.18   $266.20   $266.20  
  Purchase #7 $26.37   12.319%   $29.6185   $29.62   $29.60   $29.60  
  7 purchase totals = $1,136.34       $1,227.6750   $1,227.68   $1,227.65   $1,227.80