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 $186.25   11.483%   $207.6371   $207.64   $207.65   $207.60  
  Purchase #2 $249.43   11.625%   $278.4262   $278.43   $278.45   $278.40  
  Purchase #3 $113.33   13.432%   $128.5525   $128.55   $128.55   $128.60  
  Purchase #4 $101.53   5.132%   $106.7405   $106.74   $106.75   $106.70  
  Purchase #5 $66.67   9.374%   $72.9196   $72.92   $72.90   $72.90  
  Purchase #6 $172.94   9.167%   $188.7934   $188.79   $188.80   $188.80  
  Purchase #7 $44.67   13.631%   $50.759   $50.76   $50.75   $50.80  
  7 purchase totals = $934.82       $1,033.8283   $1,033.83   $1,033.85   $1,033.80