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 $32.57   8.319%   $35.2795   $35.28   $35.30   $35.30  
  Purchase #2 $101.43   11.721%   $113.3186   $113.32   $113.30   $113.30  
  Purchase #3 $37.26   5.543%   $39.3253   $39.33   $39.35   $39.30  
  Purchase #4 $129.29   8.509%   $140.2913   $140.29   $140.30   $140.30  
  Purchase #5 $239.29   12.632%   $269.5171   $269.52   $269.50   $269.50  
  Purchase #6 $207.88   9.341%   $227.2981   $227.30   $227.30   $227.30  
  Purchase #7 $166.47   5.659%   $175.8905   $175.89   $175.90   $175.90  
  7 purchase totals = $914.19       $1,000.9204   $1,000.93   $1,000.95   $1,000.90