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 $94.49   4.409%   $98.6561   $98.66   $98.65   $98.70  
  Purchase #2 $165.27   3.636%   $171.2792   $171.28   $171.30   $171.30  
  Purchase #3 $219.32   7.745%   $236.3063   $236.31   $236.30   $236.30  
  Purchase #4 $61.78   6.669%   $65.9001   $65.90   $65.90   $65.90  
  Purchase #5 $150.84   12.806%   $170.1566   $170.16   $170.15   $170.20  
  Purchase #6 $16.43   4.641%   $17.1925   $17.19   $17.20   $17.20  
  Purchase #7 $235.34   9.741%   $258.2645   $258.26   $258.25   $258.30  
  7 purchase totals = $943.47       $1,017.7553   $1,017.76   $1,017.75   $1,017.90