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 $46.45   13.278%   $52.6176   $52.62   $52.60   $52.60  
  Purchase #2 $180.43   10.337%   $199.081   $199.08   $199.10   $199.10  
  Purchase #3 $216.63   5.145%   $227.7756   $227.78   $227.80   $227.80  
  Purchase #4 $219.66   12.434%   $246.9725   $246.97   $246.95   $247.00  
  Purchase #5 $78.83   4.321%   $82.2362   $82.24   $82.25   $82.20  
  Purchase #6 $65.50   3.561%   $67.8325   $67.83   $67.85   $67.80  
  Purchase #7 $176.50   4.403%   $184.2713   $184.27   $184.25   $184.30  
  7 purchase totals = $984.00       $1,060.7867   $1,060.79   $1,060.80   $1,060.80