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 $238.75   5.203%   $251.1722   $251.17   $251.15   $251.20  
  Purchase #2 $186.36   4.529%   $194.8002   $194.80   $194.80   $194.80  
  Purchase #3 $111.62   9.323%   $122.0263   $122.03   $122.05   $122.00  
  Purchase #4 $49.73   12.502%   $55.9472   $55.95   $55.95   $55.90  
  Purchase #5 $207.84   3.408%   $214.9232   $214.92   $214.90   $214.90  
  Purchase #6 $147.28   9.832%   $161.7606   $161.76   $161.75   $161.80  
  Purchase #7 $52.92   12.238%   $59.3963   $59.40   $59.40   $59.40  
  7 purchase totals = $994.50       $1,060.0260   $1,060.03   $1,060.00   $1,060.00