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 $55.78   5.710%   $58.965   $58.97   $58.95   $59.00  
  Purchase #2 $186.56   13.534%   $211.809   $211.81   $211.80   $211.80  
  Purchase #3 $216.65   10.555%   $239.5174   $239.52   $239.50   $239.50  
  Purchase #4 $153.67   3.758%   $159.4449   $159.44   $159.45   $159.40  
  Purchase #5 $50.42   8.708%   $54.8106   $54.81   $54.80   $54.80  
  Purchase #6 $241.45   10.338%   $266.4111   $266.41   $266.40   $266.40  
  Purchase #7 $214.67   7.275%   $230.2872   $230.29   $230.30   $230.30  
  7 purchase totals = $1,119.20       $1,221.2452   $1,221.25   $1,221.20   $1,221.20