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 $38.34   12.182%   $43.0106   $43.01   $43.00   $43.00  
  Purchase #2 $188.84   13.745%   $214.7961   $214.80   $214.80   $214.80  
  Purchase #3 $202.80   13.192%   $229.5534   $229.55   $229.55   $229.60  
  Purchase #4 $139.33   7.852%   $150.2702   $150.27   $150.25   $150.30  
  Purchase #5 $53.86   3.801%   $55.9072   $55.91   $55.90   $55.90  
  Purchase #6 $87.27   12.559%   $98.2302   $98.23   $98.25   $98.20  
  Purchase #7 $55.92   9.499%   $61.2318   $61.23   $61.25   $61.20  
  7 purchase totals = $766.36       $852.9995   $853.00   $853.00   $853.00