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 $40.96   8.190%   $44.3146   $44.31   $44.30   $44.30  
  Purchase #2 $219.81   13.320%   $249.0887   $249.09   $249.10   $249.10  
  Purchase #3 $162.39   5.508%   $171.3344   $171.33   $171.35   $171.30  
  Purchase #4 $53.82   13.357%   $61.0087   $61.01   $61.00   $61.00  
  Purchase #5 $227.91   6.117%   $241.8513   $241.85   $241.85   $241.90  
  Purchase #6 $102.55   6.175%   $108.8825   $108.88   $108.90   $108.90  
  Purchase #7 $111.56   6.449%   $118.7545   $118.75   $118.75   $118.80  
  7 purchase totals = $919.00       $995.2347   $995.22   $995.25   $995.30