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 $93.65   13.386%   $106.186   $106.19   $106.20   $106.20  
  Purchase #2 $115.35   13.437%   $130.8496   $130.85   $130.85   $130.80  
  Purchase #3 $54.41   10.203%   $59.9615   $59.96   $59.95   $60.00  
  Purchase #4 $227.92   12.841%   $257.1872   $257.19   $257.20   $257.20  
  Purchase #5 $242.26   13.796%   $275.6822   $275.68   $275.70   $275.70  
  Purchase #6 $130.57   3.712%   $135.4168   $135.42   $135.40   $135.40  
  Purchase #7 $127.67   10.629%   $141.24   $141.24   $141.25   $141.20  
  7 purchase totals = $991.83       $1,106.5233   $1,106.53   $1,106.55   $1,106.50