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 $62.61   11.687%   $69.9272   $69.93   $69.95   $69.90  
  Purchase #2 $246.77   5.640%   $260.6878   $260.69   $260.70   $260.70  
  Purchase #3 $86.72   8.795%   $94.347   $94.35   $94.35   $94.30  
  Purchase #4 $131.26   5.304%   $138.222   $138.22   $138.20   $138.20  
  Purchase #5 $45.75   4.122%   $47.6358   $47.64   $47.65   $47.60  
  Purchase #6 $19.89   7.133%   $21.3088   $21.31   $21.30   $21.30  
  Purchase #7 $110.27   6.609%   $117.5577   $117.56   $117.55   $117.60  
  7 purchase totals = $703.27       $749.6863   $749.70   $749.70   $749.60