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 $53.43   5.804%   $56.5311   $56.53   $56.55   $56.50  
  Purchase #2 $240.29   9.803%   $263.8456   $263.85   $263.85   $263.80  
  Purchase #3 $167.30   6.416%   $178.034   $178.03   $178.05   $178.00  
  Purchase #4 $34.91   6.605%   $37.2158   $37.22   $37.20   $37.20  
  Purchase #5 $61.87   5.591%   $65.3292   $65.33   $65.35   $65.30  
  Purchase #6 $40.84   9.532%   $44.7329   $44.73   $44.75   $44.70  
  Purchase #7 $130.89   6.783%   $139.7683   $139.77   $139.75   $139.80  
  7 purchase totals = $729.53       $785.4569   $785.46   $785.50   $785.30