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 $68.39   6.524%   $72.8518   $72.85   $72.85   $72.90  
  Purchase #2 $80.27   13.421%   $91.043   $91.04   $91.05   $91.00  
  Purchase #3 $236.49   10.577%   $261.5035   $261.50   $261.50   $261.50  
  Purchase #4 $203.35   3.785%   $211.0468   $211.05   $211.05   $211.00  
  Purchase #5 $207.90   8.767%   $226.1266   $226.13   $226.15   $226.10  
  Purchase #6 $22.72   11.144%   $25.2519   $25.25   $25.25   $25.30  
  Purchase #7 $174.68   13.797%   $198.7806   $198.78   $198.80   $198.80  
  7 purchase totals = $993.80       $1,086.6042   $1,086.60   $1,086.65   $1,086.60