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 $121.69   3.579%   $126.0453   $126.05   $126.05   $126.00  
  Purchase #2 $87.92   9.398%   $96.1827   $96.18   $96.20   $96.20  
  Purchase #3 $106.58   4.483%   $111.358   $111.36   $111.35   $111.40  
  Purchase #4 $211.47   10.829%   $234.3701   $234.37   $234.35   $234.40  
  Purchase #5 $213.68   12.574%   $240.5481   $240.55   $240.55   $240.50  
  Purchase #6 $236.39   10.795%   $261.9083   $261.91   $261.90   $261.90  
  Purchase #7 $165.33   11.197%   $183.842   $183.84   $183.85   $183.80  
  7 purchase totals = $1,143.06       $1,254.2545   $1,254.26   $1,254.25   $1,254.20