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 $86.95   11.179%   $96.6701   $96.67   $96.65   $96.70  
  Purchase #2 $91.78   7.594%   $98.7498   $98.75   $98.75   $98.70  
  Purchase #3 $197.59   10.666%   $218.6649   $218.66   $218.65   $218.70  
  Purchase #4 $103.35   11.632%   $115.3717   $115.37   $115.35   $115.40  
  Purchase #5 $228.98   6.577%   $244.04   $244.04   $244.05   $244.00  
  Purchase #6 $102.51   9.655%   $112.4073   $112.41   $112.40   $112.40  
  Purchase #7 $8.25   7.321%   $8.854   $8.85   $8.85   $8.90  
  7 purchase totals = $819.41       $894.7578   $894.75   $894.70   $894.80