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 $60.43   11.596%   $67.4375   $67.44   $67.45   $67.40  
  Purchase #2 $152.68   13.797%   $173.7453   $173.75   $173.75   $173.70  
  Purchase #3 $19.93   4.262%   $20.7794   $20.78   $20.80   $20.80  
  Purchase #4 $171.90   8.306%   $186.178   $186.18   $186.20   $186.20  
  Purchase #5 $135.33   13.472%   $153.5617   $153.56   $153.55   $153.60  
  Purchase #6 $200.57   8.487%   $217.5924   $217.59   $217.60   $217.60  
  Purchase #7 $206.64   12.139%   $231.724   $231.72   $231.70   $231.70  
  7 purchase totals = $947.48       $1,051.0183   $1,051.02   $1,051.05   $1,051.00