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 $51.95   10.656%   $57.4858   $57.49   $57.50   $57.50  
  Purchase #2 $233.50   12.753%   $263.2783   $263.28   $263.30   $263.30  
  Purchase #3 $71.46   5.806%   $75.609   $75.61   $75.60   $75.60  
  Purchase #4 $154.95   3.824%   $160.8753   $160.88   $160.90   $160.90  
  Purchase #5 $22.59   10.620%   $24.9891   $24.99   $25.00   $25.00  
  Purchase #6 $147.25   11.747%   $164.5475   $164.55   $164.55   $164.50  
  Purchase #7 $102.75   11.370%   $114.4327   $114.43   $114.45   $114.40  
  7 purchase totals = $784.45       $861.2177   $861.23   $861.30   $861.20