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 $52.60   11.793%   $58.8031   $58.80   $58.80   $58.80  
  Purchase #2 $153.63   12.306%   $172.5357   $172.54   $172.55   $172.50  
  Purchase #3 $196.81   13.788%   $223.9462   $223.95   $223.95   $223.90  
  Purchase #4 $75.65   12.319%   $84.9693   $84.97   $84.95   $85.00  
  Purchase #5 $19.36   13.644%   $22.0015   $22.00   $22.00   $22.00  
  Purchase #6 $230.95   3.785%   $239.6915   $239.69   $239.70   $239.70  
  Purchase #7 $191.87   10.541%   $212.095   $212.10   $212.10   $212.10  
  7 purchase totals = $920.87       $1,014.0423   $1,014.05   $1,014.05   $1,014.00