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 $194.68   3.702%   $201.8871   $201.89   $201.90   $201.90  
  Purchase #2 $49.46   7.220%   $53.031   $53.03   $53.05   $53.00  
  Purchase #3 $33.49   9.128%   $36.547   $36.55   $36.55   $36.50  
  Purchase #4 $217.36   6.627%   $231.7644   $231.76   $231.75   $231.80  
  Purchase #5 $186.39   10.623%   $206.1902   $206.19   $206.20   $206.20  
  Purchase #6 $40.57   3.134%   $41.8415   $41.84   $41.85   $41.80  
  Purchase #7 $50.71   5.559%   $53.529   $53.53   $53.55   $53.50  
  7 purchase totals = $772.66       $824.7902   $824.79   $824.85   $824.70