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 $88.72   8.664%   $96.4067   $96.41   $96.40   $96.40  
  Purchase #2 $10.58   6.330%   $11.2497   $11.25   $11.25   $11.20  
  Purchase #3 $216.60   13.549%   $245.9471   $245.95   $245.95   $245.90  
  Purchase #4 $61.57   5.461%   $64.9323   $64.93   $64.95   $64.90  
  Purchase #5 $212.74   11.263%   $236.7009   $236.70   $236.70   $236.70  
  Purchase #6 $107.97   3.492%   $111.7403   $111.74   $111.75   $111.70  
  Purchase #7 $243.76   5.294%   $256.6647   $256.66   $256.65   $256.70  
  7 purchase totals = $941.94       $1,023.6417   $1,023.64   $1,023.65   $1,023.50