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 $113.88   3.631%   $118.015   $118.02   $118.00   $118.00  
  Purchase #2 $31.38   12.696%   $35.364   $35.36   $35.35   $35.40  
  Purchase #3 $181.30   9.852%   $199.1617   $199.16   $199.15   $199.20  
  Purchase #4 $80.79   7.315%   $86.6998   $86.70   $86.70   $86.70  
  Purchase #5 $120.65   3.461%   $124.8257   $124.83   $124.85   $124.80  
  Purchase #6 $14.35   4.641%   $15.016   $15.02   $15.00   $15.00  
  Purchase #7 $212.58   6.399%   $226.183   $226.18   $226.20   $226.20  
  7 purchase totals = $754.93       $805.2652   $805.27   $805.25   $805.30