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 $246.83   10.868%   $273.6555   $273.66   $273.65   $273.70  
  Purchase #2 $250.49   3.697%   $259.7506   $259.75   $259.75   $259.80  
  Purchase #3 $43.77   9.493%   $47.9251   $47.93   $47.95   $47.90  
  Purchase #4 $202.80   8.374%   $219.7825   $219.78   $219.80   $219.80  
  Purchase #5 $243.74   9.377%   $266.5955   $266.60   $266.60   $266.60  
  Purchase #6 $202.52   5.645%   $213.9523   $213.95   $213.95   $214.00  
  Purchase #7 $145.98   12.367%   $164.0333   $164.03   $164.05   $164.00  
  7 purchase totals = $1,336.13       $1,445.6948   $1,445.70   $1,445.75   $1,445.80