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 $91.46   3.711%   $94.8541   $94.85   $94.85   $94.90  
  Purchase #2 $246.39   9.686%   $270.2553   $270.26   $270.25   $270.30  
  Purchase #3 $164.34   8.448%   $178.2234   $178.22   $178.20   $178.20  
  Purchase #4 $21.57   3.171%   $22.254   $22.25   $22.25   $22.30  
  Purchase #5 $122.27   5.113%   $128.5217   $128.52   $128.50   $128.50  
  Purchase #6 $22.54   8.827%   $24.5296   $24.53   $24.55   $24.50  
  Purchase #7 $81.39   3.171%   $83.9709   $83.97   $83.95   $84.00  
  7 purchase totals = $749.96       $802.6090   $802.60   $802.55   $802.70