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 $103.55   11.393%   $115.3475   $115.35   $115.35   $115.30  
  Purchase #2 $170.42   13.277%   $193.0467   $193.05   $193.05   $193.00  
  Purchase #3 $93.61   10.362%   $103.3099   $103.31   $103.30   $103.30  
  Purchase #4 $36.76   6.801%   $39.26   $39.26   $39.25   $39.30  
  Purchase #5 $77.36   6.829%   $82.6429   $82.64   $82.65   $82.60  
  Purchase #6 $248.34   12.579%   $279.5787   $279.58   $279.60   $279.60  
  Purchase #7 $170.94   12.387%   $192.1143   $192.11   $192.10   $192.10  
  7 purchase totals = $900.98       $1,005.3000   $1,005.30   $1,005.30   $1,005.20