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 $47.68   6.458%   $50.7592   $50.76   $50.75   $50.80  
  Purchase #2 $239.41   7.123%   $256.4632   $256.46   $256.45   $256.50  
  Purchase #3 $219.38   6.709%   $234.0982   $234.10   $234.10   $234.10  
  Purchase #4 $33.98   7.542%   $36.5428   $36.54   $36.55   $36.50  
  Purchase #5 $236.32   11.633%   $263.8111   $263.81   $263.80   $263.80  
  Purchase #6 $210.69   4.426%   $220.0151   $220.02   $220.00   $220.00  
  Purchase #7 $153.88   12.547%   $173.1873   $173.19   $173.20   $173.20  
  7 purchase totals = $1,141.34       $1,234.8769   $1,234.88   $1,234.85   $1,234.90