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 $207.61   13.776%   $236.2104   $236.21   $236.20   $236.20  
  Purchase #2 $95.41   12.317%   $107.1616   $107.16   $107.15   $107.20  
  Purchase #3 $215.59   11.364%   $240.0896   $240.09   $240.10   $240.10  
  Purchase #4 $41.84   10.317%   $46.1566   $46.16   $46.15   $46.20  
  Purchase #5 $100.96   9.826%   $110.8803   $110.88   $110.90   $110.90  
  Purchase #6 $16.75   10.196%   $18.4578   $18.46   $18.45   $18.50  
  Purchase #7 $179.65   12.479%   $202.0685   $202.07   $202.05   $202.10  
  7 purchase totals = $857.81       $961.0248   $961.03   $961.00   $961.20