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 $24.65   7.220%   $26.4297   $26.43   $26.45   $26.40  
  Purchase #2 $63.26   10.813%   $70.1003   $70.10   $70.10   $70.10  
  Purchase #3 $55.96   3.112%   $57.7015   $57.70   $57.70   $57.70  
  Purchase #4 $75.70   7.341%   $81.2571   $81.26   $81.25   $81.30  
  Purchase #5 $128.27   4.176%   $133.6266   $133.63   $133.65   $133.60  
  Purchase #6 $228.55   8.176%   $247.2362   $247.24   $247.25   $247.20  
  Purchase #7 $139.26   7.700%   $149.983   $149.98   $150.00   $150.00  
  7 purchase totals = $715.65       $766.3344   $766.34   $766.40   $766.30