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 $182.57   13.708%   $207.5967   $207.60   $207.60   $207.60  
  Purchase #2 $100.44   3.240%   $103.6943   $103.69   $103.70   $103.70  
  Purchase #3 $235.43   3.662%   $244.0514   $244.05   $244.05   $244.10  
  Purchase #4 $25.94   12.487%   $29.1791   $29.18   $29.20   $29.20  
  Purchase #5 $233.97   8.403%   $253.6305   $253.63   $253.65   $253.60  
  Purchase #6 $141.69   12.463%   $159.3488   $159.35   $159.35   $159.30  
  Purchase #7 $68.82   9.145%   $75.1136   $75.11   $75.10   $75.10  
  7 purchase totals = $988.86       $1,072.6144   $1,072.61   $1,072.65   $1,072.60