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 $59.32   4.193%   $61.8073   $61.81   $61.80   $61.80  
  Purchase #2 $191.49   5.474%   $201.9722   $201.97   $201.95   $202.00  
  Purchase #3 $231.97   13.403%   $263.0609   $263.06   $263.05   $263.10  
  Purchase #4 $18.26   11.701%   $20.3966   $20.40   $20.40   $20.40  
  Purchase #5 $172.34   8.252%   $186.5615   $186.56   $186.55   $186.60  
  Purchase #6 $226.68   6.460%   $241.3235   $241.32   $241.30   $241.30  
  Purchase #7 $40.30   10.557%   $44.5545   $44.55   $44.55   $44.60  
  7 purchase totals = $940.36       $1,019.6765   $1,019.67   $1,019.60   $1,019.80