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 $38.64   6.109%   $41.0005   $41.00   $41.00   $41.00  
  Purchase #2 $163.56   11.194%   $181.8689   $181.87   $181.85   $181.90  
  Purchase #3 $202.74   12.733%   $228.5549   $228.55   $228.55   $228.60  
  Purchase #4 $176.99   5.420%   $186.5829   $186.58   $186.60   $186.60  
  Purchase #5 $150.71   13.655%   $171.2895   $171.29   $171.30   $171.30  
  Purchase #6 $63.89   11.358%   $71.1466   $71.15   $71.15   $71.10  
  Purchase #7 $101.59   5.375%   $107.0505   $107.05   $107.05   $107.10  
  7 purchase totals = $898.12       $987.4938   $987.49   $987.50   $987.60