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 $226.28   8.802%   $246.1972   $246.20   $246.20   $246.20  
  Purchase #2 $118.73   3.139%   $122.4569   $122.46   $122.45   $122.50  
  Purchase #3 $80.45   11.241%   $89.4934   $89.49   $89.50   $89.50  
  Purchase #4 $18.47   9.870%   $20.293   $20.29   $20.30   $20.30  
  Purchase #5 $179.83   13.819%   $204.6807   $204.68   $204.70   $204.70  
  Purchase #6 $227.72   6.798%   $243.2004   $243.20   $243.20   $243.20  
  Purchase #7 $45.77   7.448%   $49.1789   $49.18   $49.20   $49.20  
  7 purchase totals = $897.25       $975.5005   $975.50   $975.55   $975.60