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 $158.37   9.662%   $173.6717   $173.67   $173.65   $173.70  
  Purchase #2 $52.78   8.559%   $57.2974   $57.30   $57.30   $57.30  
  Purchase #3 $60.33   7.610%   $64.9211   $64.92   $64.90   $64.90  
  Purchase #4 $203.45   13.762%   $231.4488   $231.45   $231.45   $231.40  
  Purchase #5 $241.56   12.544%   $271.8613   $271.86   $271.85   $271.90  
  Purchase #6 $162.61   12.703%   $183.2663   $183.27   $183.25   $183.30  
  Purchase #7 $30.74   5.493%   $32.4285   $32.43   $32.45   $32.40  
  7 purchase totals = $909.84       $1,014.8951   $1,014.90   $1,014.85   $1,014.90