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 $146.87   6.148%   $155.8996   $155.90   $155.90   $155.90  
  Purchase #2 $190.54   10.502%   $210.5505   $210.55   $210.55   $210.60  
  Purchase #3 $96.55   11.856%   $107.997   $108.00   $108.00   $108.00  
  Purchase #4 $245.38   12.341%   $275.6623   $275.66   $275.65   $275.70  
  Purchase #5 $195.25   5.355%   $205.7056   $205.71   $205.70   $205.70  
  Purchase #6 $226.93   3.452%   $234.7636   $234.76   $234.75   $234.80  
  Purchase #7 $198.59   3.643%   $205.8246   $205.82   $205.80   $205.80  
  7 purchase totals = $1,300.11       $1,396.4032   $1,396.40   $1,396.35   $1,396.50