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 $220.60   6.325%   $234.553   $234.55   $234.55   $234.60  
  Purchase #2 $243.59   12.823%   $274.8255   $274.83   $274.85   $274.80  
  Purchase #3 $56.87   11.744%   $63.5488   $63.55   $63.55   $63.50  
  Purchase #4 $215.33   9.267%   $235.2846   $235.28   $235.30   $235.30  
  Purchase #5 $32.73   6.624%   $34.898   $34.90   $34.90   $34.90  
  Purchase #6 $184.53   8.559%   $200.3239   $200.32   $200.30   $200.30  
  Purchase #7 $26.28   9.498%   $28.7761   $28.78   $28.80   $28.80  
  7 purchase totals = $979.93       $1,072.2099   $1,072.21   $1,072.25   $1,072.20