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 $181.47   11.844%   $202.9633   $202.96   $202.95   $203.00  
  Purchase #2 $91.28   5.859%   $96.6281   $96.63   $96.65   $96.60  
  Purchase #3 $49.28   6.505%   $52.4857   $52.49   $52.50   $52.50  
  Purchase #4 $176.29   8.386%   $191.0737   $191.07   $191.05   $191.10  
  Purchase #5 $153.80   4.389%   $160.5503   $160.55   $160.55   $160.60  
  Purchase #6 $145.54   4.381%   $151.9161   $151.92   $151.90   $151.90  
  Purchase #7 $173.54   11.545%   $193.5752   $193.58   $193.60   $193.60  
  7 purchase totals = $971.20       $1,049.1924   $1,049.20   $1,049.20   $1,049.30