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 $86.49   9.588%   $94.7827   $94.78   $94.80   $94.80  
  Purchase #2 $101.57   13.791%   $115.5775   $115.58   $115.60   $115.60  
  Purchase #3 $212.51   8.785%   $231.179   $231.18   $231.20   $231.20  
  Purchase #4 $213.60   12.126%   $239.5011   $239.50   $239.50   $239.50  
  Purchase #5 $56.47   7.768%   $60.8566   $60.86   $60.85   $60.90  
  Purchase #6 $156.35   8.138%   $169.0738   $169.07   $169.05   $169.10  
  Purchase #7 $106.98   3.607%   $110.8388   $110.84   $110.85   $110.80  
  7 purchase totals = $933.97       $1,021.8095   $1,021.81   $1,021.85   $1,021.90