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 $244.54   9.672%   $268.1919   $268.19   $268.20   $268.20  
  Purchase #2 $154.64   6.659%   $164.9375   $164.94   $164.95   $164.90  
  Purchase #3 $94.53   12.278%   $106.1364   $106.14   $106.15   $106.10  
  Purchase #4 $240.73   13.429%   $273.0576   $273.06   $273.05   $273.10  
  Purchase #5 $91.61   4.839%   $96.043   $96.04   $96.05   $96.00  
  Purchase #6 $25.54   4.601%   $26.7151   $26.72   $26.70   $26.70  
  Purchase #7 $182.39   11.270%   $202.9454   $202.95   $202.95   $202.90  
  7 purchase totals = $1,033.98       $1,138.0269   $1,138.04   $1,138.05   $1,137.90