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 $39.86   10.595%   $44.0832   $44.08   $44.10   $44.10  
  Purchase #2 $232.85   4.449%   $243.2095   $243.21   $243.20   $243.20  
  Purchase #3 $242.50   12.217%   $272.1262   $272.13   $272.15   $272.10  
  Purchase #4 $58.49   7.500%   $62.8768   $62.88   $62.90   $62.90  
  Purchase #5 $74.56   11.254%   $82.951   $82.95   $82.95   $83.00  
  Purchase #6 $193.81   7.781%   $208.8904   $208.89   $208.90   $208.90  
  Purchase #7 $133.45   5.257%   $140.4655   $140.47   $140.45   $140.50  
  7 purchase totals = $975.52       $1,054.6026   $1,054.61   $1,054.65   $1,054.70