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 $97.35   7.167%   $104.3271   $104.33   $104.35   $104.30  
  Purchase #2 $128.87   5.172%   $135.5352   $135.54   $135.55   $135.50  
  Purchase #3 $34.95   3.214%   $36.0733   $36.07   $36.05   $36.10  
  Purchase #4 $219.49   12.748%   $247.4706   $247.47   $247.45   $247.50  
  Purchase #5 $127.70   8.320%   $138.3246   $138.32   $138.30   $138.30  
  Purchase #6 $205.58   5.358%   $216.595   $216.60   $216.60   $216.60  
  Purchase #7 $162.35   12.268%   $182.2671   $182.27   $182.25   $182.30  
  7 purchase totals = $976.29       $1,060.5929   $1,060.60   $1,060.55   $1,060.60