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 $128.35   4.632%   $134.2952   $134.30   $134.30   $134.30  
  Purchase #2 $203.96   9.795%   $223.9379   $223.94   $223.95   $223.90  
  Purchase #3 $202.93   7.274%   $217.6911   $217.69   $217.70   $217.70  
  Purchase #4 $143.54   12.765%   $161.8629   $161.86   $161.85   $161.90  
  Purchase #5 $181.34   5.235%   $190.8331   $190.83   $190.85   $190.80  
  Purchase #6 $96.69   10.388%   $106.7342   $106.73   $106.75   $106.70  
  Purchase #7 $103.99   8.637%   $112.9716   $112.97   $112.95   $113.00  
  7 purchase totals = $1,060.80       $1,148.3260   $1,148.32   $1,148.35   $1,148.30