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 $83.68   11.202%   $93.0538   $93.05   $93.05   $93.10  
  Purchase #2 $91.72   5.463%   $96.7307   $96.73   $96.75   $96.70  
  Purchase #3 $44.34   4.658%   $46.4054   $46.41   $46.40   $46.40  
  Purchase #4 $31.86   6.707%   $33.9969   $34.00   $34.00   $34.00  
  Purchase #5 $240.46   13.822%   $273.6964   $273.70   $273.70   $273.70  
  Purchase #6 $10.40   6.131%   $11.0376   $11.04   $11.05   $11.00  
  Purchase #7 $128.31   4.870%   $134.5587   $134.56   $134.55   $134.60  
  7 purchase totals = $630.77       $689.4795   $689.49   $689.50   $689.50