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 $34.61   10.830%   $38.3583   $38.36   $38.35   $38.40  
  Purchase #2 $240.33   11.451%   $267.8502   $267.85   $267.85   $267.90  
  Purchase #3 $106.29   7.658%   $114.4297   $114.43   $114.45   $114.40  
  Purchase #4 $244.40   12.731%   $275.5146   $275.51   $275.50   $275.50  
  Purchase #5 $22.95   5.585%   $24.2318   $24.23   $24.25   $24.20  
  Purchase #6 $212.38   10.235%   $234.1171   $234.12   $234.10   $234.10  
  Purchase #7 $118.73   8.645%   $128.9942   $128.99   $129.00   $129.00  
  7 purchase totals = $979.69       $1,083.4959   $1,083.49   $1,083.50   $1,083.50