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 $201.82   12.321%   $226.6862   $226.69   $226.70   $226.70  
  Purchase #2 $162.67   11.866%   $181.9724   $181.97   $181.95   $182.00  
  Purchase #3 $60.79   6.293%   $64.6155   $64.62   $64.60   $64.60  
  Purchase #4 $53.68   12.402%   $60.3374   $60.34   $60.35   $60.30  
  Purchase #5 $52.50   12.748%   $59.1927   $59.19   $59.20   $59.20  
  Purchase #6 $247.53   3.156%   $255.342   $255.34   $255.35   $255.30  
  Purchase #7 $170.53   13.444%   $193.4561   $193.46   $193.45   $193.50  
  7 purchase totals = $949.52       $1,041.6023   $1,041.61   $1,041.60   $1,041.60