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 $68.47   11.323%   $76.2229   $76.22   $76.20   $76.20  
  Purchase #2 $210.44   8.331%   $227.9718   $227.97   $227.95   $228.00  
  Purchase #3 $219.48   8.340%   $237.7846   $237.78   $237.80   $237.80  
  Purchase #4 $108.25   9.861%   $118.9245   $118.92   $118.90   $118.90  
  Purchase #5 $240.71   9.404%   $263.3464   $263.35   $263.35   $263.30  
  Purchase #6 $246.31   12.213%   $276.3918   $276.39   $276.40   $276.40  
  Purchase #7 $81.66   8.255%   $88.401   $88.40   $88.40   $88.40  
  7 purchase totals = $1,175.32       $1,289.0430   $1,289.03   $1,289.00   $1,289.00