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 $43.73   3.213%   $45.135   $45.14   $45.15   $45.10  
  Purchase #2 $203.35   8.611%   $220.8605   $220.86   $220.85   $220.90  
  Purchase #3 $155.40   8.213%   $168.163   $168.16   $168.15   $168.20  
  Purchase #4 $32.95   8.293%   $35.6825   $35.68   $35.70   $35.70  
  Purchase #5 $138.75   4.832%   $145.4544   $145.45   $145.45   $145.50  
  Purchase #6 $232.68   4.867%   $244.0045   $244.00   $244.00   $244.00  
  Purchase #7 $174.69   12.432%   $196.4075   $196.41   $196.40   $196.40  
  7 purchase totals = $981.55       $1,055.7074   $1,055.70   $1,055.70   $1,055.80