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 $68.70   7.385%   $73.7735   $73.77   $73.75   $73.80  
  Purchase #2 $236.39   3.580%   $244.8528   $244.85   $244.85   $244.90  
  Purchase #3 $147.30   3.506%   $152.4643   $152.46   $152.45   $152.50  
  Purchase #4 $239.40   3.702%   $248.2626   $248.26   $248.25   $248.30  
  Purchase #5 $24.95   8.608%   $27.0977   $27.10   $27.10   $27.10  
  Purchase #6 $242.36   4.789%   $253.9666   $253.97   $253.95   $254.00  
  Purchase #7 $37.94   3.436%   $39.2436   $39.24   $39.25   $39.20  
  7 purchase totals = $997.04       $1,039.6611   $1,039.65   $1,039.60   $1,039.80