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 $69.70   8.520%   $75.6384   $75.64   $75.65   $75.60  
  Purchase #2 $71.26   11.157%   $79.2105   $79.21   $79.20   $79.20  
  Purchase #3 $155.62   5.611%   $164.3518   $164.35   $164.35   $164.40  
  Purchase #4 $240.84   7.598%   $259.139   $259.14   $259.15   $259.10  
  Purchase #5 $183.37   11.735%   $204.8885   $204.89   $204.90   $204.90  
  Purchase #6 $167.76   5.484%   $176.96   $176.96   $176.95   $177.00  
  Purchase #7 $139.35   12.395%   $156.6224   $156.62   $156.60   $156.60  
  7 purchase totals = $1,027.90       $1,116.8106   $1,116.81   $1,116.80   $1,116.80