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 $67.29   9.637%   $73.7747   $73.77   $73.75   $73.80  
  Purchase #2 $248.58   9.249%   $271.5712   $271.57   $271.55   $271.60  
  Purchase #3 $9.82   4.480%   $10.2599   $10.26   $10.25   $10.30  
  Purchase #4 $219.77   11.758%   $245.6106   $245.61   $245.60   $245.60  
  Purchase #5 $26.61   11.737%   $29.7332   $29.73   $29.75   $29.70  
  Purchase #6 $214.85   13.124%   $243.0469   $243.05   $243.05   $243.00  
  Purchase #7 $173.72   7.307%   $186.4137   $186.41   $186.40   $186.40  
  7 purchase totals = $960.64       $1,060.4102   $1,060.40   $1,060.35   $1,060.40