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 $58.28   7.483%   $62.6411   $62.64   $62.65   $62.60  
  Purchase #2 $108.79   13.304%   $123.2634   $123.26   $123.25   $123.30  
  Purchase #3 $59.80   12.713%   $67.4024   $67.40   $67.40   $67.40  
  Purchase #4 $186.46   9.746%   $204.6324   $204.63   $204.65   $204.60  
  Purchase #5 $14.64   11.486%   $16.3216   $16.32   $16.30   $16.30  
  Purchase #6 $213.47   8.577%   $231.7793   $231.78   $231.80   $231.80  
  Purchase #7 $161.95   3.776%   $168.0652   $168.07   $168.05   $168.10  
  7 purchase totals = $803.39       $874.1054   $874.10   $874.10   $874.10