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 $91.43   12.712%   $103.0526   $103.05   $103.05   $103.10  
  Purchase #2 $172.46   12.628%   $194.2382   $194.24   $194.25   $194.20  
  Purchase #3 $117.70   3.235%   $121.5076   $121.51   $121.50   $121.50  
  Purchase #4 $103.86   8.446%   $112.632   $112.63   $112.65   $112.60  
  Purchase #5 $67.43   3.107%   $69.5251   $69.53   $69.55   $69.50  
  Purchase #6 $250.98   12.584%   $282.5633   $282.56   $282.55   $282.60  
  Purchase #7 $215.43   12.537%   $242.4385   $242.44   $242.45   $242.40  
  7 purchase totals = $1,019.29       $1,125.9573   $1,125.96   $1,126.00   $1,125.90