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 $32.72   7.528%   $35.1832   $35.18   $35.20   $35.20  
  Purchase #2 $121.74   5.242%   $128.1216   $128.12   $128.10   $128.10  
  Purchase #3 $84.43   7.334%   $90.6221   $90.62   $90.60   $90.60  
  Purchase #4 $108.36   3.465%   $112.1147   $112.11   $112.10   $112.10  
  Purchase #5 $145.43   11.235%   $161.7691   $161.77   $161.75   $161.80  
  Purchase #6 $17.93   9.356%   $19.6075   $19.61   $19.60   $19.60  
  Purchase #7 $92.54   3.559%   $95.8335   $95.83   $95.85   $95.80  
  7 purchase totals = $603.15       $643.2517   $643.24   $643.20   $643.20