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 $246.49   9.439%   $269.7562   $269.76   $269.75   $269.80  
  Purchase #2 $63.99   12.121%   $71.7462   $71.75   $71.75   $71.70  
  Purchase #3 $192.67   6.330%   $204.866   $204.87   $204.85   $204.90  
  Purchase #4 $101.80   10.695%   $112.6875   $112.69   $112.70   $112.70  
  Purchase #5 $153.33   7.301%   $164.5246   $164.52   $164.50   $164.50  
  Purchase #6 $190.41   5.659%   $201.1853   $201.19   $201.20   $201.20  
  Purchase #7 $140.48   9.163%   $153.3522   $153.35   $153.35   $153.40  
  7 purchase totals = $1,089.17       $1,178.1180   $1,178.13   $1,178.10   $1,178.20