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 $192.78   7.338%   $206.9262   $206.93   $206.95   $206.90  
  Purchase #2 $21.56   8.811%   $23.4597   $23.46   $23.45   $23.50  
  Purchase #3 $85.43   13.764%   $97.1886   $97.19   $97.20   $97.20  
  Purchase #4 $190.84   13.356%   $216.3286   $216.33   $216.35   $216.30  
  Purchase #5 $241.59   10.263%   $266.3844   $266.38   $266.40   $266.40  
  Purchase #6 $124.42   12.409%   $139.8593   $139.86   $139.85   $139.90  
  Purchase #7 $105.96   6.127%   $112.4522   $112.45   $112.45   $112.50  
  7 purchase totals = $962.58       $1,062.5990   $1,062.60   $1,062.65   $1,062.70