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 $67.49   3.576%   $69.9034   $69.90   $69.90   $69.90  
  Purchase #2 $167.84   8.256%   $181.6969   $181.70   $181.70   $181.70  
  Purchase #3 $172.49   11.773%   $192.7972   $192.80   $192.80   $192.80  
  Purchase #4 $213.41   5.342%   $224.8104   $224.81   $224.80   $224.80  
  Purchase #5 $179.60   5.534%   $189.5391   $189.54   $189.55   $189.50  
  Purchase #6 $134.84   6.462%   $143.5534   $143.55   $143.55   $143.60  
  Purchase #7 $69.33   6.442%   $73.7962   $73.80   $73.80   $73.80  
  7 purchase totals = $1,005.00       $1,076.0966   $1,076.10   $1,076.10   $1,076.10