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 $62.29   11.131%   $69.2235   $69.22   $69.20   $69.20  
  Purchase #2 $11.62   3.117%   $11.9822   $11.98   $12.00   $12.00  
  Purchase #3 $90.94   12.719%   $102.5067   $102.51   $102.50   $102.50  
  Purchase #4 $99.82   10.579%   $110.38   $110.38   $110.40   $110.40  
  Purchase #5 $198.59   3.241%   $205.0263   $205.03   $205.05   $205.00  
  Purchase #6 $39.86   6.421%   $42.4194   $42.42   $42.40   $42.40  
  Purchase #7 $230.98   9.242%   $252.3272   $252.33   $252.35   $252.30  
  7 purchase totals = $734.10       $793.8653   $793.87   $793.90   $793.80