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 $59.47   11.183%   $66.1205   $66.12   $66.10   $66.10  
  Purchase #2 $201.85   13.383%   $228.8636   $228.86   $228.85   $228.90  
  Purchase #3 $174.45   6.628%   $186.0125   $186.01   $186.00   $186.00  
  Purchase #4 $50.63   6.650%   $53.9969   $54.00   $54.00   $54.00  
  Purchase #5 $70.31   11.274%   $78.2367   $78.24   $78.25   $78.20  
  Purchase #6 $99.54   3.620%   $103.1433   $103.14   $103.15   $103.10  
  Purchase #7 $26.82   7.539%   $28.842   $28.84   $28.85   $28.80  
  7 purchase totals = $683.07       $745.2155   $745.21   $745.20   $745.10