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 $183.52   11.620%   $204.845   $204.85   $204.85   $204.80  
  Purchase #2 $249.84   11.825%   $279.3836   $279.38   $279.40   $279.40  
  Purchase #3 $67.71   13.630%   $76.9389   $76.94   $76.95   $76.90  
  Purchase #4 $128.79   9.542%   $141.0791   $141.08   $141.10   $141.10  
  Purchase #5 $120.67   13.280%   $136.695   $136.70   $136.70   $136.70  
  Purchase #6 $151.95   13.527%   $172.5043   $172.50   $172.50   $172.50  
  Purchase #7 $7.61   8.596%   $8.2642   $8.26   $8.25   $8.30  
  7 purchase totals = $910.09       $1,019.7101   $1,019.71   $1,019.75   $1,019.70