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 $32.29   7.573%   $34.7353   $34.74   $34.75   $34.70  
  Purchase #2 $188.74   11.564%   $210.5659   $210.57   $210.55   $210.60  
  Purchase #3 $148.88   3.333%   $153.8422   $153.84   $153.85   $153.80  
  Purchase #4 $233.57   3.560%   $241.8851   $241.89   $241.90   $241.90  
  Purchase #5 $86.81   11.653%   $96.926   $96.93   $96.95   $96.90  
  Purchase #6 $228.41   6.207%   $242.5874   $242.59   $242.60   $242.60  
  Purchase #7 $5.96   9.732%   $6.54   $6.54   $6.55   $6.50  
  7 purchase totals = $924.66       $987.0819   $987.10   $987.15   $987.00