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 $32.32   7.611%   $34.7799   $34.78   $34.80   $34.80  
  Purchase #2 $52.55   6.764%   $56.1045   $56.10   $56.10   $56.10  
  Purchase #3 $16.58   13.450%   $18.81   $18.81   $18.80   $18.80  
  Purchase #4 $119.96   3.588%   $124.2642   $124.26   $124.25   $124.30  
  Purchase #5 $248.37   13.410%   $281.6764   $281.68   $281.70   $281.70  
  Purchase #6 $86.77   4.161%   $90.3805   $90.38   $90.40   $90.40  
  Purchase #7 $171.74   5.640%   $181.4261   $181.43   $181.45   $181.40  
  7 purchase totals = $728.29       $787.4416   $787.44   $787.50   $787.50