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 $84.25   12.258%   $94.5774   $94.58   $94.60   $94.60  
  Purchase #2 $100.38   5.814%   $106.2161   $106.22   $106.20   $106.20  
  Purchase #3 $155.57   8.538%   $168.8526   $168.85   $168.85   $168.90  
  Purchase #4 $219.26   4.219%   $228.5106   $228.51   $228.50   $228.50  
  Purchase #5 $196.62   12.549%   $221.2938   $221.29   $221.30   $221.30  
  Purchase #6 $226.25   5.452%   $238.5852   $238.59   $238.60   $238.60  
  Purchase #7 $218.62   10.334%   $241.2122   $241.21   $241.20   $241.20  
  7 purchase totals = $1,200.95       $1,299.2479   $1,299.25   $1,299.25   $1,299.30