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 $173.72   5.516%   $183.3024   $183.30   $183.30   $183.30  
  Purchase #2 $101.99   9.290%   $111.4649   $111.46   $111.45   $111.50  
  Purchase #3 $223.44   5.818%   $236.4397   $236.44   $236.45   $236.40  
  Purchase #4 $108.53   4.196%   $113.0839   $113.08   $113.10   $113.10  
  Purchase #5 $101.69   9.112%   $110.956   $110.96   $110.95   $111.00  
  Purchase #6 $233.30   6.833%   $249.2414   $249.24   $249.25   $249.20  
  Purchase #7 $175.27   11.444%   $195.3279   $195.33   $195.35   $195.30  
  7 purchase totals = $1,117.94       $1,199.8162   $1,199.81   $1,199.85   $1,199.80