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 $91.62   5.159%   $96.3467   $96.35   $96.35   $96.30  
  Purchase #2 $168.78   5.137%   $177.4502   $177.45   $177.45   $177.50  
  Purchase #3 $97.73   5.861%   $103.458   $103.46   $103.45   $103.50  
  Purchase #4 $42.27   9.543%   $46.3038   $46.30   $46.30   $46.30  
  Purchase #5 $245.73   3.243%   $253.699   $253.70   $253.70   $253.70  
  Purchase #6 $6.74   12.579%   $7.5878   $7.59   $7.60   $7.60  
  Purchase #7 $101.96   5.526%   $107.5943   $107.59   $107.60   $107.60  
  7 purchase totals = $754.83       $792.4398   $792.44   $792.45   $792.50