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 $34.64   6.319%   $36.8289   $36.83   $36.85   $36.80  
  Purchase #2 $221.57   6.233%   $235.3805   $235.38   $235.40   $235.40  
  Purchase #3 $71.81   5.179%   $75.529   $75.53   $75.55   $75.50  
  Purchase #4 $15.87   6.232%   $16.859   $16.86   $16.85   $16.90  
  Purchase #5 $156.88   12.762%   $176.901   $176.90   $176.90   $176.90  
  Purchase #6 $88.98   4.145%   $92.6682   $92.67   $92.65   $92.70  
  Purchase #7 $57.81   5.197%   $60.8144   $60.81   $60.80   $60.80  
  7 purchase totals = $647.56       $694.9810   $694.98   $695.00   $695.00