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 $180.53   7.325%   $193.7538   $193.75   $193.75   $193.80  
  Purchase #2 $128.27   10.201%   $141.3548   $141.35   $141.35   $141.40  
  Purchase #3 $174.46   13.456%   $197.9353   $197.94   $197.95   $197.90  
  Purchase #4 $230.57   6.516%   $245.5939   $245.59   $245.60   $245.60  
  Purchase #5 $166.60   4.155%   $173.5222   $173.52   $173.50   $173.50  
  Purchase #6 $78.64   7.491%   $84.5309   $84.53   $84.55   $84.50  
  Purchase #7 $102.58   12.255%   $115.1512   $115.15   $115.15   $115.20  
  7 purchase totals = $1,061.65       $1,151.8421   $1,151.83   $1,151.85   $1,151.90