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 $94.41   8.608%   $102.5368   $102.54   $102.55   $102.50  
  Purchase #2 $181.57   6.485%   $193.3448   $193.34   $193.35   $193.30  
  Purchase #3 $226.48   13.394%   $256.8147   $256.81   $256.80   $256.80  
  Purchase #4 $42.98   8.645%   $46.6956   $46.70   $46.70   $46.70  
  Purchase #5 $104.73   4.661%   $109.6115   $109.61   $109.60   $109.60  
  Purchase #6 $26.27   10.815%   $29.1111   $29.11   $29.10   $29.10  
  Purchase #7 $57.98   7.459%   $62.3047   $62.30   $62.30   $62.30  
  7 purchase totals = $734.42       $800.4192   $800.41   $800.40   $800.30