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 $62.38   8.242%   $67.5214   $67.52   $67.50   $67.50  
  Purchase #2 $227.55   9.294%   $248.6985   $248.70   $248.70   $248.70  
  Purchase #3 $235.37   12.470%   $264.7206   $264.72   $264.70   $264.70  
  Purchase #4 $108.43   13.219%   $122.7634   $122.76   $122.75   $122.80  
  Purchase #5 $5.98   7.209%   $6.4111   $6.41   $6.40   $6.40  
  Purchase #6 $81.34   7.435%   $87.3876   $87.39   $87.40   $87.40  
  Purchase #7 $208.89   13.363%   $236.804   $236.80   $236.80   $236.80  
  7 purchase totals = $929.94       $1,034.3066   $1,034.30   $1,034.25   $1,034.30