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 $69.94   9.167%   $76.3514   $76.35   $76.35   $76.40  
  Purchase #2 $226.27   9.784%   $248.4083   $248.41   $248.40   $248.40  
  Purchase #3 $27.84   7.323%   $29.8787   $29.88   $29.90   $29.90  
  Purchase #4 $83.45   4.865%   $87.5098   $87.51   $87.50   $87.50  
  Purchase #5 $236.78   13.747%   $269.3301   $269.33   $269.35   $269.30  
  Purchase #6 $231.95   13.487%   $263.2331   $263.23   $263.25   $263.20  
  Purchase #7 $45.52   3.243%   $46.9962   $47.00   $47.00   $47.00  
  7 purchase totals = $921.75       $1,021.7076   $1,021.71   $1,021.75   $1,021.70