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 $184.35   8.809%   $200.5894   $200.59   $200.60   $200.60  
  Purchase #2 $229.94   6.262%   $244.3388   $244.34   $244.35   $244.30  
  Purchase #3 $207.59   13.708%   $236.0464   $236.05   $236.05   $236.00  
  Purchase #4 $110.33   6.747%   $117.774   $117.77   $117.75   $117.80  
  Purchase #5 $210.28   13.513%   $238.6951   $238.70   $238.70   $238.70  
  Purchase #6 $44.56   13.582%   $50.6121   $50.61   $50.60   $50.60  
  Purchase #7 $158.27   9.157%   $172.7628   $172.76   $172.75   $172.80  
  7 purchase totals = $1,145.32       $1,260.8186   $1,260.82   $1,260.80   $1,260.80