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 $55.56   4.858%   $58.2591   $58.26   $58.25   $58.30  
  Purchase #2 $232.77   11.245%   $258.945   $258.95   $258.95   $258.90  
  Purchase #3 $13.84   3.151%   $14.2761   $14.28   $14.30   $14.30  
  Purchase #4 $238.88   7.819%   $257.558   $257.56   $257.55   $257.60  
  Purchase #5 $236.58   9.771%   $259.6962   $259.70   $259.70   $259.70  
  Purchase #6 $24.91   3.793%   $25.8548   $25.85   $25.85   $25.90  
  Purchase #7 $133.46   9.203%   $145.7423   $145.74   $145.75   $145.70  
  7 purchase totals = $936.00       $1,020.3315   $1,020.34   $1,020.35   $1,020.40