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 $61.67   8.254%   $66.7602   $66.76   $66.75   $66.80  
  Purchase #2 $231.81   5.312%   $244.1237   $244.12   $244.10   $244.10  
  Purchase #3 $105.53   13.868%   $120.1649   $120.16   $120.15   $120.20  
  Purchase #4 $186.81   10.855%   $207.0882   $207.09   $207.10   $207.10  
  Purchase #5 $138.64   8.692%   $150.6906   $150.69   $150.70   $150.70  
  Purchase #6 $177.82   4.423%   $185.685   $185.69   $185.70   $185.70  
  Purchase #7 $150.89   13.238%   $170.8648   $170.86   $170.85   $170.90  
  7 purchase totals = $1,053.17       $1,145.3774   $1,145.37   $1,145.35   $1,145.50