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 $55.90   8.118%   $60.438   $60.44   $60.45   $60.40  
  Purchase #2 $69.93   7.251%   $75.0006   $75.00   $75.00   $75.00  
  Purchase #3 $86.50   8.354%   $93.7262   $93.73   $93.75   $93.70  
  Purchase #4 $69.30   12.584%   $78.0207   $78.02   $78.00   $78.00  
  Purchase #5 $60.84   4.227%   $63.4117   $63.41   $63.40   $63.40  
  Purchase #6 $49.57   5.257%   $52.1759   $52.18   $52.20   $52.20  
  Purchase #7 $128.65   6.801%   $137.3995   $137.40   $137.40   $137.40  
  7 purchase totals = $520.69       $560.1726   $560.18   $560.20   $560.10