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 $190.35   10.871%   $211.0429   $211.04   $211.05   $211.00  
  Purchase #2 $93.39   3.505%   $96.6633   $96.66   $96.65   $96.70  
  Purchase #3 $83.45   4.731%   $87.398   $87.40   $87.40   $87.40  
  Purchase #4 $107.75   10.658%   $119.234   $119.23   $119.25   $119.20  
  Purchase #5 $183.86   12.165%   $206.2266   $206.23   $206.25   $206.20  
  Purchase #6 $232.58   11.304%   $258.8708   $258.87   $258.85   $258.90  
  Purchase #7 $64.99   9.523%   $71.179   $71.18   $71.20   $71.20  
  7 purchase totals = $956.37       $1,050.6146   $1,050.61   $1,050.65   $1,050.60