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 $47.49   7.831%   $51.2089   $51.21   $51.20   $51.20  
  Purchase #2 $118.84   3.648%   $123.1753   $123.18   $123.20   $123.20  
  Purchase #3 $153.88   12.603%   $173.2735   $173.27   $173.25   $173.30  
  Purchase #4 $197.36   3.159%   $203.5946   $203.59   $203.60   $203.60  
  Purchase #5 $134.87   5.406%   $142.1611   $142.16   $142.15   $142.20  
  Purchase #6 $250.90   5.516%   $264.7396   $264.74   $264.75   $264.70  
  Purchase #7 $84.55   3.447%   $87.4644   $87.46   $87.45   $87.50  
  7 purchase totals = $987.89       $1,045.6174   $1,045.61   $1,045.60   $1,045.70