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 $53.56   6.109%   $56.832   $56.83   $56.85   $56.80  
  Purchase #2 $20.27   11.650%   $22.6315   $22.63   $22.65   $22.60  
  Purchase #3 $38.58   10.355%   $42.575   $42.58   $42.60   $42.60  
  Purchase #4 $169.95   13.603%   $193.0683   $193.07   $193.05   $193.10  
  Purchase #5 $49.86   8.190%   $53.9435   $53.94   $53.95   $53.90  
  Purchase #6 $179.37   11.158%   $199.3841   $199.38   $199.40   $199.40  
  Purchase #7 $22.55   12.229%   $25.3076   $25.31   $25.30   $25.30  
  7 purchase totals = $534.14       $593.7420   $593.74   $593.80   $593.70