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 $60.66   8.133%   $65.5935   $65.59   $65.60   $65.60  
  Purchase #2 $247.25   8.681%   $268.7138   $268.71   $268.70   $268.70  
  Purchase #3 $113.28   13.859%   $128.9795   $128.98   $129.00   $129.00  
  Purchase #4 $51.58   7.578%   $55.4887   $55.49   $55.50   $55.50  
  Purchase #5 $160.60   13.673%   $182.5588   $182.56   $182.55   $182.60  
  Purchase #6 $162.27   12.127%   $181.9485   $181.95   $181.95   $181.90  
  Purchase #7 $156.30   11.338%   $174.0213   $174.02   $174.00   $174.00  
  7 purchase totals = $951.94       $1,057.3041   $1,057.30   $1,057.30   $1,057.30