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 $183.60   7.127%   $196.6852   $196.69   $196.70   $196.70  
  Purchase #2 $69.91   6.325%   $74.3318   $74.33   $74.35   $74.30  
  Purchase #3 $128.73   7.335%   $138.1723   $138.17   $138.15   $138.20  
  Purchase #4 $64.58   5.313%   $68.0111   $68.01   $68.00   $68.00  
  Purchase #5 $190.40   7.234%   $204.1735   $204.17   $204.15   $204.20  
  Purchase #6 $152.60   4.322%   $159.1954   $159.20   $159.20   $159.20  
  Purchase #7 $165.42   10.519%   $182.8205   $182.82   $182.80   $182.80  
  7 purchase totals = $955.24       $1,023.3898   $1,023.39   $1,023.35   $1,023.40