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 $195.85   11.607%   $218.5823   $218.58   $218.60   $218.60  
  Purchase #2 $39.42   4.839%   $41.3275   $41.33   $41.35   $41.30  
  Purchase #3 $151.69   3.728%   $157.345   $157.35   $157.35   $157.30  
  Purchase #4 $153.85   9.244%   $168.0719   $168.07   $168.05   $168.10  
  Purchase #5 $234.33   9.632%   $256.9007   $256.90   $256.90   $256.90  
  Purchase #6 $243.99   9.517%   $267.2105   $267.21   $267.20   $267.20  
  Purchase #7 $232.57   11.475%   $259.2574   $259.26   $259.25   $259.30  
  7 purchase totals = $1,251.70       $1,368.6953   $1,368.70   $1,368.70   $1,368.70